Merge branch 'sb/oid-object-info'

[git] / convert.c

#define NO_THE_INDEX_COMPATIBILITY_MACROS
#include "cache.h"
#include "config.h"
#include "attr.h"
#include "run-command.h"
#include "quote.h"
#include "sigchain.h"
#include "pkt-line.h"
#include "sub-process.h"
#include "utf8.h"

/*
 * convert.c - convert a file when checking it out and checking it in.
 *
 * This should use the pathname to decide on whether it wants to do some
 * more interesting conversions (automatic gzip/unzip, general format
 * conversions etc etc), but by default it just does automatic CRLF<->LF
 * translation when the "text" attribute or "auto_crlf" option is set.
 */

/* Stat bits: When BIN is set, the txt bits are unset */
#define CONVERT_STAT_BITS_TXT_LF    0x1
#define CONVERT_STAT_BITS_TXT_CRLF  0x2
#define CONVERT_STAT_BITS_BIN       0x4

enum crlf_action {
        CRLF_UNDEFINED,
        CRLF_BINARY,
        CRLF_TEXT,
        CRLF_TEXT_INPUT,
        CRLF_TEXT_CRLF,
        CRLF_AUTO,
        CRLF_AUTO_INPUT,
        CRLF_AUTO_CRLF
};

struct text_stat {
        /* NUL, CR, LF and CRLF counts */
        unsigned nul, lonecr, lonelf, crlf;

        /* These are just approximations! */
        unsigned printable, nonprintable;
};

static void gather_stats(const char *buf, unsigned long size, struct text_stat *stats)
{
        unsigned long i;

        memset(stats, 0, sizeof(*stats));

        for (i = 0; i < size; i++) {
                unsigned char c = buf[i];
                if (c == '\r') {
                        if (i+1 < size && buf[i+1] == '\n') {
                                stats->crlf++;
                                i++;
                        } else
                                stats->lonecr++;
                        continue;
                }
                if (c == '\n') {
                        stats->lonelf++;
                        continue;
                }
                if (c == 127)
                        /* DEL */
                        stats->nonprintable++;
                else if (c < 32) {
                        switch (c) {
                                /* BS, HT, ESC and FF */
                        case '\b': case '\t': case '\033': case '\014':
                                stats->printable++;
                                break;
                        case 0:
                                stats->nul++;
                                /* fall through */
                        default:
                                stats->nonprintable++;
                        }
                }
                else
                        stats->printable++;
        }

        /* If file ends with EOF then don't count this EOF as non-printable. */
        if (size >= 1 && buf[size-1] == '\032')
                stats->nonprintable--;
}

/*
 * The same heuristics as diff.c::mmfile_is_binary()
 * We treat files with bare CR as binary
 */
static int convert_is_binary(unsigned long size, const struct text_stat *stats)
{
        if (stats->lonecr)
                return 1;
        if (stats->nul)
                return 1;
        if ((stats->printable >> 7) < stats->nonprintable)
                return 1;
        return 0;
}

static unsigned int gather_convert_stats(const char *data, unsigned long size)
{
        struct text_stat stats;
        int ret = 0;
        if (!data || !size)
                return 0;
        gather_stats(data, size, &stats);
        if (convert_is_binary(size, &stats))
                ret |= CONVERT_STAT_BITS_BIN;
        if (stats.crlf)
                ret |= CONVERT_STAT_BITS_TXT_CRLF;
        if (stats.lonelf)
                ret |=  CONVERT_STAT_BITS_TXT_LF;

        return ret;
}

static const char *gather_convert_stats_ascii(const char *data, unsigned long size)
{
        unsigned int convert_stats = gather_convert_stats(data, size);

        if (convert_stats & CONVERT_STAT_BITS_BIN)
                return "-text";
        switch (convert_stats) {
        case CONVERT_STAT_BITS_TXT_LF:
                return "lf";
        case CONVERT_STAT_BITS_TXT_CRLF:
                return "crlf";
        case CONVERT_STAT_BITS_TXT_LF | CONVERT_STAT_BITS_TXT_CRLF:
                return "mixed";
        default:
                return "none";
        }
}

const char *get_cached_convert_stats_ascii(const struct index_state *istate,
                                           const char *path)
{
        const char *ret;
        unsigned long sz;
        void *data = read_blob_data_from_index(istate, path, &sz);
        ret = gather_convert_stats_ascii(data, sz);
        free(data);
        return ret;
}

const char *get_wt_convert_stats_ascii(const char *path)
{
        const char *ret = "";
        struct strbuf sb = STRBUF_INIT;
        if (strbuf_read_file(&sb, path, 0) >= 0)
                ret = gather_convert_stats_ascii(sb.buf, sb.len);
        strbuf_release(&sb);
        return ret;
}

static int text_eol_is_crlf(void)
{
        if (auto_crlf == AUTO_CRLF_TRUE)
                return 1;
        else if (auto_crlf == AUTO_CRLF_INPUT)
                return 0;
        if (core_eol == EOL_CRLF)
                return 1;
        if (core_eol == EOL_UNSET && EOL_NATIVE == EOL_CRLF)
                return 1;
        return 0;
}

static enum eol output_eol(enum crlf_action crlf_action)
{
        switch (crlf_action) {
        case CRLF_BINARY:
                return EOL_UNSET;
        case CRLF_TEXT_CRLF:
                return EOL_CRLF;
        case CRLF_TEXT_INPUT:
                return EOL_LF;
        case CRLF_UNDEFINED:
        case CRLF_AUTO_CRLF:
                return EOL_CRLF;
        case CRLF_AUTO_INPUT:
                return EOL_LF;
        case CRLF_TEXT:
        case CRLF_AUTO:
                /* fall through */
                return text_eol_is_crlf() ? EOL_CRLF : EOL_LF;
        }
        warning("Illegal crlf_action %d\n", (int)crlf_action);
        return core_eol;
}

static void check_global_conv_flags_eol(const char *path, enum crlf_action crlf_action,
                            struct text_stat *old_stats, struct text_stat *new_stats,
                            int conv_flags)
{
        if (old_stats->crlf && !new_stats->crlf ) {
                /*
                 * CRLFs would not be restored by checkout
                 */
                if (conv_flags & CONV_EOL_RNDTRP_DIE)
                        die(_("CRLF would be replaced by LF in %s."), path);
                else if (conv_flags & CONV_EOL_RNDTRP_WARN)
                        warning(_("CRLF will be replaced by LF in %s.\n"
                                  "The file will have its original line"
                                  " endings in your working directory."), path);
        } else if (old_stats->lonelf && !new_stats->lonelf ) {
                /*
                 * CRLFs would be added by checkout
                 */
                if (conv_flags & CONV_EOL_RNDTRP_DIE)
                        die(_("LF would be replaced by CRLF in %s"), path);
                else if (conv_flags & CONV_EOL_RNDTRP_WARN)
                        warning(_("LF will be replaced by CRLF in %s.\n"
                                  "The file will have its original line"
                                  " endings in your working directory."), path);
        }
}

static int has_crlf_in_index(const struct index_state *istate, const char *path)
{
        unsigned long sz;
        void *data;
        const char *crp;
        int has_crlf = 0;

        data = read_blob_data_from_index(istate, path, &sz);
        if (!data)
                return 0;

        crp = memchr(data, '\r', sz);
        if (crp) {
                unsigned int ret_stats;
                ret_stats = gather_convert_stats(data, sz);
                if (!(ret_stats & CONVERT_STAT_BITS_BIN) &&
                    (ret_stats & CONVERT_STAT_BITS_TXT_CRLF))
                        has_crlf = 1;
        }
        free(data);
        return has_crlf;
}

static int will_convert_lf_to_crlf(size_t len, struct text_stat *stats,
                                   enum crlf_action crlf_action)
{
        if (output_eol(crlf_action) != EOL_CRLF)
                return 0;
        /* No "naked" LF? Nothing to convert, regardless. */
        if (!stats->lonelf)
                return 0;

        if (crlf_action == CRLF_AUTO || crlf_action == CRLF_AUTO_INPUT || crlf_action == CRLF_AUTO_CRLF) {
                /* If we have any CR or CRLF line endings, we do not touch it */
                /* This is the new safer autocrlf-handling */
                if (stats->lonecr || stats->crlf)
                        return 0;

                if (convert_is_binary(len, stats))
                        return 0;
        }
        return 1;

}

static int validate_encoding(const char *path, const char *enc,
                      const char *data, size_t len, int die_on_error)
{
        /* We only check for UTF here as UTF?? can be an alias for UTF-?? */
        if (istarts_with(enc, "UTF")) {
                /*
                 * Check for detectable errors in UTF encodings
                 */
                if (has_prohibited_utf_bom(enc, data, len)) {
                        const char *error_msg = _(
                                "BOM is prohibited in '%s' if encoded as %s");
                        /*
                         * This advice is shown for UTF-??BE and UTF-??LE encodings.
                         * We cut off the last two characters of the encoding name
                         * to generate the encoding name suitable for BOMs.
                         */
                        const char *advise_msg = _(
                                "The file '%s' contains a byte order "
                                "mark (BOM). Please use UTF-%s as "
                                "working-tree-encoding.");
                        const char *stripped = NULL;
                        char *upper = xstrdup_toupper(enc);
                        upper[strlen(upper)-2] = '\0';
                        if (!skip_prefix(upper, "UTF-", &stripped))
                                skip_prefix(stripped, "UTF", &stripped);
                        advise(advise_msg, path, stripped);
                        free(upper);
                        if (die_on_error)
                                die(error_msg, path, enc);
                        else {
                                return error(error_msg, path, enc);
                        }

                } else if (is_missing_required_utf_bom(enc, data, len)) {
                        const char *error_msg = _(
                                "BOM is required in '%s' if encoded as %s");
                        const char *advise_msg = _(
                                "The file '%s' is missing a byte order "
                                "mark (BOM). Please use UTF-%sBE or UTF-%sLE "
                                "(depending on the byte order) as "
                                "working-tree-encoding.");
                        const char *stripped = NULL;
                        char *upper = xstrdup_toupper(enc);
                        if (!skip_prefix(upper, "UTF-", &stripped))
                                skip_prefix(stripped, "UTF", &stripped);
                        advise(advise_msg, path, stripped, stripped);
                        free(upper);
                        if (die_on_error)
                                die(error_msg, path, enc);
                        else {
                                return error(error_msg, path, enc);
                        }
                }

        }
        return 0;
}

static void trace_encoding(const char *context, const char *path,
                           const char *encoding, const char *buf, size_t len)
{
        static struct trace_key coe = TRACE_KEY_INIT(WORKING_TREE_ENCODING);
        struct strbuf trace = STRBUF_INIT;
        int i;

        strbuf_addf(&trace, "%s (%s, considered %s):\n", context, path, encoding);
        for (i = 0; i < len && buf; ++i) {
                strbuf_addf(
                        &trace,"| \e[2m%2i:\e[0m %2x \e[2m%c\e[0m%c",
                        i,
                        (unsigned char) buf[i],
                        (buf[i] > 32 && buf[i] < 127 ? buf[i] : ' '),
                        ((i+1) % 8 && (i+1) < len ? ' ' : '\n')
                );
        }
        strbuf_addchars(&trace, '\n', 1);

        trace_strbuf(&coe, &trace);
        strbuf_release(&trace);
}

static int check_roundtrip(const char *enc_name)
{
        /*
         * check_roundtrip_encoding contains a string of comma and/or
         * space separated encodings (eg. "UTF-16, ASCII, CP1125").
         * Search for the given encoding in that string.
         */
        const char *found = strcasestr(check_roundtrip_encoding, enc_name);
        const char *next;
        int len;
        if (!found)
                return 0;
        next = found + strlen(enc_name);
        len = strlen(check_roundtrip_encoding);
        return (found && (
                        /*
                         * check that the found encoding is at the
                         * beginning of check_roundtrip_encoding or
                         * that it is prefixed with a space or comma
                         */
                        found == check_roundtrip_encoding || (
                                (isspace(found[-1]) || found[-1] == ',')
                        )
                ) && (
                        /*
                         * check that the found encoding is at the
                         * end of check_roundtrip_encoding or
                         * that it is suffixed with a space or comma
                         */
                        next == check_roundtrip_encoding + len || (
                                next < check_roundtrip_encoding + len &&
                                (isspace(next[0]) || next[0] == ',')
                        )
                ));
}

static const char *default_encoding = "UTF-8";

static int encode_to_git(const char *path, const char *src, size_t src_len,
                         struct strbuf *buf, const char *enc, int conv_flags)
{
        char *dst;
        int dst_len;
        int die_on_error = conv_flags & CONV_WRITE_OBJECT;

        /*
         * No encoding is specified or there is nothing to encode.
         * Tell the caller that the content was not modified.
         */
        if (!enc || (src && !src_len))
                return 0;

        /*
         * Looks like we got called from "would_convert_to_git()".
         * This means Git wants to know if it would encode (= modify!)
         * the content. Let's answer with "yes", since an encoding was
         * specified.
         */
        if (!buf && !src)
                return 1;

        if (validate_encoding(path, enc, src, src_len, die_on_error))
                return 0;

        trace_encoding("source", path, enc, src, src_len);
        dst = reencode_string_len(src, src_len, default_encoding, enc,
                                  &dst_len);
        if (!dst) {
                /*
                 * We could add the blob "as-is" to Git. However, on checkout
                 * we would try to reencode to the original encoding. This
                 * would fail and we would leave the user with a messed-up
                 * working tree. Let's try to avoid this by screaming loud.
                 */
                const char* msg = _("failed to encode '%s' from %s to %s");
                if (die_on_error)
                        die(msg, path, enc, default_encoding);
                else {
                        error(msg, path, enc, default_encoding);
                        return 0;
                }
        }
        trace_encoding("destination", path, default_encoding, dst, dst_len);

        /*
         * UTF supports lossless conversion round tripping [1] and conversions
         * between UTF and other encodings are mostly round trip safe as
         * Unicode aims to be a superset of all other character encodings.
         * However, certain encodings (e.g. SHIFT-JIS) are known to have round
         * trip issues [2]. Check the round trip conversion for all encodings
         * listed in core.checkRoundtripEncoding.
         *
         * The round trip check is only performed if content is written to Git.
         * This ensures that no information is lost during conversion to/from
         * the internal UTF-8 representation.
         *
         * Please note, the code below is not tested because I was not able to
         * generate a faulty round trip without an iconv error. Iconv errors
         * are already caught above.
         *
         * [1] http://unicode.org/faq/utf_bom.html#gen2
         * [2] https://support.microsoft.com/en-us/help/170559/prb-conversion-problem-between-shift-jis-and-unicode
         */
        if (die_on_error && check_roundtrip(enc)) {
                char *re_src;
                int re_src_len;

                re_src = reencode_string_len(dst, dst_len,
                                             enc, default_encoding,
                                             &re_src_len);

                trace_printf("Checking roundtrip encoding for %s...\n", enc);
                trace_encoding("reencoded source", path, enc,
                               re_src, re_src_len);

                if (!re_src || src_len != re_src_len ||
                    memcmp(src, re_src, src_len)) {
                        const char* msg = _("encoding '%s' from %s to %s and "
                                            "back is not the same");
                        die(msg, path, enc, default_encoding);
                }

                free(re_src);
        }

        strbuf_attach(buf, dst, dst_len, dst_len + 1);
        return 1;
}

static int encode_to_worktree(const char *path, const char *src, size_t src_len,
                              struct strbuf *buf, const char *enc)
{
        char *dst;
        int dst_len;

        /*
         * No encoding is specified or there is nothing to encode.
         * Tell the caller that the content was not modified.
         */
        if (!enc || (src && !src_len))
                return 0;

        dst = reencode_string_len(src, src_len, enc, default_encoding,
                                  &dst_len);
        if (!dst) {
                error("failed to encode '%s' from %s to %s",
                        path, default_encoding, enc);
                return 0;
        }

        strbuf_attach(buf, dst, dst_len, dst_len + 1);
        return 1;
}

static int crlf_to_git(const struct index_state *istate,
                       const char *path, const char *src, size_t len,
                       struct strbuf *buf,
                       enum crlf_action crlf_action, int conv_flags)
{
        struct text_stat stats;
        char *dst;
        int convert_crlf_into_lf;

        if (crlf_action == CRLF_BINARY ||
            (src && !len))
                return 0;

        /*
         * If we are doing a dry-run and have no source buffer, there is
         * nothing to analyze; we must assume we would convert.
         */
        if (!buf && !src)
                return 1;

        gather_stats(src, len, &stats);
        /* Optimization: No CRLF? Nothing to convert, regardless. */
        convert_crlf_into_lf = !!stats.crlf;

        if (crlf_action == CRLF_AUTO || crlf_action == CRLF_AUTO_INPUT || crlf_action == CRLF_AUTO_CRLF) {
                if (convert_is_binary(len, &stats))
                        return 0;
                /*
                 * If the file in the index has any CR in it, do not
                 * convert.  This is the new safer autocrlf handling,
                 * unless we want to renormalize in a merge or
                 * cherry-pick.
                 */
                if ((!(conv_flags & CONV_EOL_RENORMALIZE)) &&
                    has_crlf_in_index(istate, path))
                        convert_crlf_into_lf = 0;
        }
        if (((conv_flags & CONV_EOL_RNDTRP_WARN) ||
             ((conv_flags & CONV_EOL_RNDTRP_DIE) && len))) {
                struct text_stat new_stats;
                memcpy(&new_stats, &stats, sizeof(new_stats));
                /* simulate "git add" */
                if (convert_crlf_into_lf) {
                        new_stats.lonelf += new_stats.crlf;
                        new_stats.crlf = 0;
                }
                /* simulate "git checkout" */
                if (will_convert_lf_to_crlf(len, &new_stats, crlf_action)) {
                        new_stats.crlf += new_stats.lonelf;
                        new_stats.lonelf = 0;
                }
                check_global_conv_flags_eol(path, crlf_action, &stats, &new_stats, conv_flags);
        }
        if (!convert_crlf_into_lf)
                return 0;

        /*
         * At this point all of our source analysis is done, and we are sure we
         * would convert. If we are in dry-run mode, we can give an answer.
         */
        if (!buf)
                return 1;

        /* only grow if not in place */
        if (strbuf_avail(buf) + buf->len < len)
                strbuf_grow(buf, len - buf->len);
        dst = buf->buf;
        if (crlf_action == CRLF_AUTO || crlf_action == CRLF_AUTO_INPUT || crlf_action == CRLF_AUTO_CRLF) {
                /*
                 * If we guessed, we already know we rejected a file with
                 * lone CR, and we can strip a CR without looking at what
                 * follow it.
                 */
                do {
                        unsigned char c = *src++;
                        if (c != '\r')
                                *dst++ = c;
                } while (--len);
        } else {
                do {
                        unsigned char c = *src++;
                        if (! (c == '\r' && (1 < len && *src == '\n')))
                                *dst++ = c;
                } while (--len);
        }
        strbuf_setlen(buf, dst - buf->buf);
        return 1;
}

static int crlf_to_worktree(const char *path, const char *src, size_t len,
                            struct strbuf *buf, enum crlf_action crlf_action)
{
        char *to_free = NULL;
        struct text_stat stats;

        if (!len || output_eol(crlf_action) != EOL_CRLF)
                return 0;

        gather_stats(src, len, &stats);
        if (!will_convert_lf_to_crlf(len, &stats, crlf_action))
                return 0;

        /* are we "faking" in place editing ? */
        if (src == buf->buf)
                to_free = strbuf_detach(buf, NULL);

        strbuf_grow(buf, len + stats.lonelf);
        for (;;) {
                const char *nl = memchr(src, '\n', len);
                if (!nl)
                        break;
                if (nl > src && nl[-1] == '\r') {
                        strbuf_add(buf, src, nl + 1 - src);
                } else {
                        strbuf_add(buf, src, nl - src);
                        strbuf_addstr(buf, "\r\n");
                }
                len -= nl + 1 - src;
                src  = nl + 1;
        }
        strbuf_add(buf, src, len);

        free(to_free);
        return 1;
}

struct filter_params {
        const char *src;
        unsigned long size;
        int fd;
        const char *cmd;
        const char *path;
};

static int filter_buffer_or_fd(int in, int out, void *data)
{
        /*
         * Spawn cmd and feed the buffer contents through its stdin.
         */
        struct child_process child_process = CHILD_PROCESS_INIT;
        struct filter_params *params = (struct filter_params *)data;
        int write_err, status;
        const char *argv[] = { NULL, NULL };

        /* apply % substitution to cmd */
        struct strbuf cmd = STRBUF_INIT;
        struct strbuf path = STRBUF_INIT;
        struct strbuf_expand_dict_entry dict[] = {
                { "f", NULL, },
                { NULL, NULL, },
        };

        /* quote the path to preserve spaces, etc. */
        sq_quote_buf(&path, params->path);
        dict[0].value = path.buf;

        /* expand all %f with the quoted path */
        strbuf_expand(&cmd, params->cmd, strbuf_expand_dict_cb, &dict);
        strbuf_release(&path);

        argv[0] = cmd.buf;

        child_process.argv = argv;
        child_process.use_shell = 1;
        child_process.in = -1;
        child_process.out = out;

        if (start_command(&child_process)) {
                strbuf_release(&cmd);
                return error("cannot fork to run external filter '%s'", params->cmd);
        }

        sigchain_push(SIGPIPE, SIG_IGN);

        if (params->src) {
                write_err = (write_in_full(child_process.in,
                                           params->src, params->size) < 0);
                if (errno == EPIPE)
                        write_err = 0;
        } else {
                write_err = copy_fd(params->fd, child_process.in);
                if (write_err == COPY_WRITE_ERROR && errno == EPIPE)
                        write_err = 0;
        }

        if (close(child_process.in))
                write_err = 1;
        if (write_err)
                error("cannot feed the input to external filter '%s'", params->cmd);

        sigchain_pop(SIGPIPE);

        status = finish_command(&child_process);
        if (status)
                error("external filter '%s' failed %d", params->cmd, status);

        strbuf_release(&cmd);
        return (write_err || status);
}

static int apply_single_file_filter(const char *path, const char *src, size_t len, int fd,
                        struct strbuf *dst, const char *cmd)
{
        /*
         * Create a pipeline to have the command filter the buffer's
         * contents.
         *
         * (child --> cmd) --> us
         */
        int err = 0;
        struct strbuf nbuf = STRBUF_INIT;
        struct async async;
        struct filter_params params;

        memset(&async, 0, sizeof(async));
        async.proc = filter_buffer_or_fd;
        async.data = &params;
        async.out = -1;
        params.src = src;
        params.size = len;
        params.fd = fd;
        params.cmd = cmd;
        params.path = path;

        fflush(NULL);
        if (start_async(&async))
                return 0;       /* error was already reported */

        if (strbuf_read(&nbuf, async.out, len) < 0) {
                err = error("read from external filter '%s' failed", cmd);
        }
        if (close(async.out)) {
                err = error("read from external filter '%s' failed", cmd);
        }
        if (finish_async(&async)) {
                err = error("external filter '%s' failed", cmd);
        }

        if (!err) {
                strbuf_swap(dst, &nbuf);
        }
        strbuf_release(&nbuf);
        return !err;
}

#define CAP_CLEAN    (1u<<0)
#define CAP_SMUDGE   (1u<<1)
#define CAP_DELAY    (1u<<2)

struct cmd2process {
        struct subprocess_entry subprocess; /* must be the first member! */
        unsigned int supported_capabilities;
};

static int subprocess_map_initialized;
static struct hashmap subprocess_map;

static int start_multi_file_filter_fn(struct subprocess_entry *subprocess)
{
        static int versions[] = {2, 0};
        static struct subprocess_capability capabilities[] = {
                { "clean",  CAP_CLEAN  },
                { "smudge", CAP_SMUDGE },
                { "delay",  CAP_DELAY  },
                { NULL, 0 }
        };
        struct cmd2process *entry = (struct cmd2process *)subprocess;
        return subprocess_handshake(subprocess, "git-filter", versions, NULL,
                                    capabilities,
                                    &entry->supported_capabilities);
}

static void handle_filter_error(const struct strbuf *filter_status,
                                struct cmd2process *entry,
                                const unsigned int wanted_capability) {
        if (!strcmp(filter_status->buf, "error"))
                ; /* The filter signaled a problem with the file. */
        else if (!strcmp(filter_status->buf, "abort") && wanted_capability) {
                /*
                 * The filter signaled a permanent problem. Don't try to filter
                 * files with the same command for the lifetime of the current
                 * Git process.
                 */
                 entry->supported_capabilities &= ~wanted_capability;
        } else {
                /*
                 * Something went wrong with the protocol filter.
                 * Force shutdown and restart if another blob requires filtering.
                 */
                error("external filter '%s' failed", entry->subprocess.cmd);
                subprocess_stop(&subprocess_map, &entry->subprocess);
                free(entry);
        }
}

static int apply_multi_file_filter(const char *path, const char *src, size_t len,
                                   int fd, struct strbuf *dst, const char *cmd,
                                   const unsigned int wanted_capability,
                                   struct delayed_checkout *dco)
{
        int err;
        int can_delay = 0;
        struct cmd2process *entry;
        struct child_process *process;
        struct strbuf nbuf = STRBUF_INIT;
        struct strbuf filter_status = STRBUF_INIT;
        const char *filter_type;

        if (!subprocess_map_initialized) {
                subprocess_map_initialized = 1;
                hashmap_init(&subprocess_map, cmd2process_cmp, NULL, 0);
                entry = NULL;
        } else {
                entry = (struct cmd2process *)subprocess_find_entry(&subprocess_map, cmd);
        }

        fflush(NULL);

        if (!entry) {
                entry = xmalloc(sizeof(*entry));
                entry->supported_capabilities = 0;

                if (subprocess_start(&subprocess_map, &entry->subprocess, cmd, start_multi_file_filter_fn)) {
                        free(entry);
                        return 0;
                }
        }
        process = &entry->subprocess.process;

        if (!(entry->supported_capabilities & wanted_capability))
                return 0;

        if (wanted_capability & CAP_CLEAN)
                filter_type = "clean";
        else if (wanted_capability & CAP_SMUDGE)
                filter_type = "smudge";
        else
                die("unexpected filter type");

        sigchain_push(SIGPIPE, SIG_IGN);

        assert(strlen(filter_type) < LARGE_PACKET_DATA_MAX - strlen("command=\n"));
        err = packet_write_fmt_gently(process->in, "command=%s\n", filter_type);
        if (err)
                goto done;

        err = strlen(path) > LARGE_PACKET_DATA_MAX - strlen("pathname=\n");
        if (err) {
                error("path name too long for external filter");
                goto done;
        }

        err = packet_write_fmt_gently(process->in, "pathname=%s\n", path);
        if (err)
                goto done;

        if ((entry->supported_capabilities & CAP_DELAY) &&
            dco && dco->state == CE_CAN_DELAY) {
                can_delay = 1;
                err = packet_write_fmt_gently(process->in, "can-delay=1\n");
                if (err)
                        goto done;
        }

        err = packet_flush_gently(process->in);
        if (err)
                goto done;

        if (fd >= 0)
                err = write_packetized_from_fd(fd, process->in);
        else
                err = write_packetized_from_buf(src, len, process->in);
        if (err)
                goto done;

        err = subprocess_read_status(process->out, &filter_status);
        if (err)
                goto done;

        if (can_delay && !strcmp(filter_status.buf, "delayed")) {
                string_list_insert(&dco->filters, cmd);
                string_list_insert(&dco->paths, path);
        } else {
                /* The filter got the blob and wants to send us a response. */
                err = strcmp(filter_status.buf, "success");
                if (err)
                        goto done;

                err = read_packetized_to_strbuf(process->out, &nbuf) < 0;
                if (err)
                        goto done;

                err = subprocess_read_status(process->out, &filter_status);
                if (err)
                        goto done;

                err = strcmp(filter_status.buf, "success");
        }

done:
        sigchain_pop(SIGPIPE);

        if (err)
                handle_filter_error(&filter_status, entry, wanted_capability);
        else
                strbuf_swap(dst, &nbuf);
        strbuf_release(&nbuf);
        return !err;
}


int async_query_available_blobs(const char *cmd, struct string_list *available_paths)
{
        int err;
        char *line;
        struct cmd2process *entry;
        struct child_process *process;
        struct strbuf filter_status = STRBUF_INIT;

        assert(subprocess_map_initialized);
        entry = (struct cmd2process *)subprocess_find_entry(&subprocess_map, cmd);
        if (!entry) {
                error("external filter '%s' is not available anymore although "
                      "not all paths have been filtered", cmd);
                return 0;
        }
        process = &entry->subprocess.process;
        sigchain_push(SIGPIPE, SIG_IGN);

        err = packet_write_fmt_gently(
                process->in, "command=list_available_blobs\n");
        if (err)
                goto done;

        err = packet_flush_gently(process->in);
        if (err)
                goto done;

        while ((line = packet_read_line(process->out, NULL))) {
                const char *path;
                if (skip_prefix(line, "pathname=", &path))
                        string_list_insert(available_paths, xstrdup(path));
                else
                        ; /* ignore unknown keys */
        }

        err = subprocess_read_status(process->out, &filter_status);
        if (err)
                goto done;

        err = strcmp(filter_status.buf, "success");

done:
        sigchain_pop(SIGPIPE);

        if (err)
                handle_filter_error(&filter_status, entry, 0);
        return !err;
}

static struct convert_driver {
        const char *name;
        struct convert_driver *next;
        const char *smudge;
        const char *clean;
        const char *process;
        int required;
} *user_convert, **user_convert_tail;

static int apply_filter(const char *path, const char *src, size_t len,
                        int fd, struct strbuf *dst, struct convert_driver *drv,
                        const unsigned int wanted_capability,
                        struct delayed_checkout *dco)
{
        const char *cmd = NULL;

        if (!drv)
                return 0;

        if (!dst)
                return 1;

        if ((wanted_capability & CAP_CLEAN) && !drv->process && drv->clean)
                cmd = drv->clean;
        else if ((wanted_capability & CAP_SMUDGE) && !drv->process && drv->smudge)
                cmd = drv->smudge;

        if (cmd && *cmd)
                return apply_single_file_filter(path, src, len, fd, dst, cmd);
        else if (drv->process && *drv->process)
                return apply_multi_file_filter(path, src, len, fd, dst,
                        drv->process, wanted_capability, dco);

        return 0;
}

static int read_convert_config(const char *var, const char *value, void *cb)
{
        const char *key, *name;
        int namelen;
        struct convert_driver *drv;

        /*
         * External conversion drivers are configured using
         * "filter.<name>.variable".
         */
        if (parse_config_key(var, "filter", &name, &namelen, &key) < 0 || !name)
                return 0;
        for (drv = user_convert; drv; drv = drv->next)
                if (!strncmp(drv->name, name, namelen) && !drv->name[namelen])
                        break;
        if (!drv) {
                drv = xcalloc(1, sizeof(struct convert_driver));
                drv->name = xmemdupz(name, namelen);
                *user_convert_tail = drv;
                user_convert_tail = &(drv->next);
        }

        /*
         * filter.<name>.smudge and filter.<name>.clean specifies
         * the command line:
         *
         *      command-line
         *
         * The command-line will not be interpolated in any way.
         */

        if (!strcmp("smudge", key))
                return git_config_string(&drv->smudge, var, value);

        if (!strcmp("clean", key))
                return git_config_string(&drv->clean, var, value);

        if (!strcmp("process", key))
                return git_config_string(&drv->process, var, value);

        if (!strcmp("required", key)) {
                drv->required = git_config_bool(var, value);
                return 0;
        }

        return 0;
}

static int count_ident(const char *cp, unsigned long size)
{
        /*
         * "$Id: 0000000000000000000000000000000000000000 $" <=> "$Id$"
         */
        int cnt = 0;
        char ch;

        while (size) {
                ch = *cp++;
                size--;
                if (ch != '$')
                        continue;
                if (size < 3)
                        break;
                if (memcmp("Id", cp, 2))
                        continue;
                ch = cp[2];
                cp += 3;
                size -= 3;
                if (ch == '$')
                        cnt++; /* $Id$ */
                if (ch != ':')
                        continue;

                /*
                 * "$Id: ... "; scan up to the closing dollar sign and discard.
                 */
                while (size) {
                        ch = *cp++;
                        size--;
                        if (ch == '$') {
                                cnt++;
                                break;
                        }
                        if (ch == '\n')
                                break;
                }
        }
        return cnt;
}

static int ident_to_git(const char *path, const char *src, size_t len,
                        struct strbuf *buf, int ident)
{
        char *dst, *dollar;

        if (!ident || (src && !count_ident(src, len)))
                return 0;

        if (!buf)
                return 1;

        /* only grow if not in place */
        if (strbuf_avail(buf) + buf->len < len)
                strbuf_grow(buf, len - buf->len);
        dst = buf->buf;
        for (;;) {
                dollar = memchr(src, '$', len);
                if (!dollar)
                        break;
                memmove(dst, src, dollar + 1 - src);
                dst += dollar + 1 - src;
                len -= dollar + 1 - src;
                src  = dollar + 1;

                if (len > 3 && !memcmp(src, "Id:", 3)) {
                        dollar = memchr(src + 3, '$', len - 3);
                        if (!dollar)
                                break;
                        if (memchr(src + 3, '\n', dollar - src - 3)) {
                                /* Line break before the next dollar. */
                                continue;
                        }

                        memcpy(dst, "Id$", 3);
                        dst += 3;
                        len -= dollar + 1 - src;
                        src  = dollar + 1;
                }
        }
        memmove(dst, src, len);
        strbuf_setlen(buf, dst + len - buf->buf);
        return 1;
}

static int ident_to_worktree(const char *path, const char *src, size_t len,
                             struct strbuf *buf, int ident)
{
        struct object_id oid;
        char *to_free = NULL, *dollar, *spc;
        int cnt;

        if (!ident)
                return 0;

        cnt = count_ident(src, len);
        if (!cnt)
                return 0;

        /* are we "faking" in place editing ? */
        if (src == buf->buf)
                to_free = strbuf_detach(buf, NULL);
        hash_object_file(src, len, "blob", &oid);

        strbuf_grow(buf, len + cnt * (the_hash_algo->hexsz + 3));
        for (;;) {
                /* step 1: run to the next '$' */
                dollar = memchr(src, '$', len);
                if (!dollar)
                        break;
                strbuf_add(buf, src, dollar + 1 - src);
                len -= dollar + 1 - src;
                src  = dollar + 1;

                /* step 2: does it looks like a bit like Id:xxx$ or Id$ ? */
                if (len < 3 || memcmp("Id", src, 2))
                        continue;

                /* step 3: skip over Id$ or Id:xxxxx$ */
                if (src[2] == '$') {
                        src += 3;
                        len -= 3;
                } else if (src[2] == ':') {
                        /*
                         * It's possible that an expanded Id has crept its way into the
                         * repository, we cope with that by stripping the expansion out.
                         * This is probably not a good idea, since it will cause changes
                         * on checkout, which won't go away by stash, but let's keep it
                         * for git-style ids.
                         */
                        dollar = memchr(src + 3, '$', len - 3);
                        if (!dollar) {
                                /* incomplete keyword, no more '$', so just quit the loop */
                                break;
                        }

                        if (memchr(src + 3, '\n', dollar - src - 3)) {
                                /* Line break before the next dollar. */
                                continue;
                        }

                        spc = memchr(src + 4, ' ', dollar - src - 4);
                        if (spc && spc < dollar-1) {
                                /* There are spaces in unexpected places.
                                 * This is probably an id from some other
                                 * versioning system. Keep it for now.
                                 */
                                continue;
                        }

                        len -= dollar + 1 - src;
                        src  = dollar + 1;
                } else {
                        /* it wasn't a "Id$" or "Id:xxxx$" */
                        continue;
                }

                /* step 4: substitute */
                strbuf_addstr(buf, "Id: ");
                strbuf_addstr(buf, oid_to_hex(&oid));
                strbuf_addstr(buf, " $");
        }
        strbuf_add(buf, src, len);

        free(to_free);
        return 1;
}

static const char *git_path_check_encoding(struct attr_check_item *check)
{
        const char *value = check->value;

        if (ATTR_UNSET(value) || !strlen(value))
                return NULL;

        if (ATTR_TRUE(value) || ATTR_FALSE(value)) {
                die(_("true/false are no valid working-tree-encodings"));
        }

        /* Don't encode to the default encoding */
        if (same_encoding(value, default_encoding))
                return NULL;

        return value;
}

static enum crlf_action git_path_check_crlf(struct attr_check_item *check)
{
        const char *value = check->value;

        if (ATTR_TRUE(value))
                return CRLF_TEXT;
        else if (ATTR_FALSE(value))
                return CRLF_BINARY;
        else if (ATTR_UNSET(value))
                ;
        else if (!strcmp(value, "input"))
                return CRLF_TEXT_INPUT;
        else if (!strcmp(value, "auto"))
                return CRLF_AUTO;
        return CRLF_UNDEFINED;
}

static enum eol git_path_check_eol(struct attr_check_item *check)
{
        const char *value = check->value;

        if (ATTR_UNSET(value))
                ;
        else if (!strcmp(value, "lf"))
                return EOL_LF;
        else if (!strcmp(value, "crlf"))
                return EOL_CRLF;
        return EOL_UNSET;
}

static struct convert_driver *git_path_check_convert(struct attr_check_item *check)
{
        const char *value = check->value;
        struct convert_driver *drv;

        if (ATTR_TRUE(value) || ATTR_FALSE(value) || ATTR_UNSET(value))
                return NULL;
        for (drv = user_convert; drv; drv = drv->next)
                if (!strcmp(value, drv->name))
                        return drv;
        return NULL;
}

static int git_path_check_ident(struct attr_check_item *check)
{
        const char *value = check->value;

        return !!ATTR_TRUE(value);
}

struct conv_attrs {
        struct convert_driver *drv;
        enum crlf_action attr_action; /* What attr says */
        enum crlf_action crlf_action; /* When no attr is set, use core.autocrlf */
        int ident;
        const char *working_tree_encoding; /* Supported encoding or default encoding if NULL */
};

static void convert_attrs(struct conv_attrs *ca, const char *path)
{
        static struct attr_check *check;

        if (!check) {
                check = attr_check_initl("crlf", "ident", "filter",
                                         "eol", "text", "working-tree-encoding",
                                         NULL);
                user_convert_tail = &user_convert;
                git_config(read_convert_config, NULL);
        }

        if (!git_check_attr(path, check)) {
                struct attr_check_item *ccheck = check->items;
                ca->crlf_action = git_path_check_crlf(ccheck + 4);
                if (ca->crlf_action == CRLF_UNDEFINED)
                        ca->crlf_action = git_path_check_crlf(ccheck + 0);
                ca->ident = git_path_check_ident(ccheck + 1);
                ca->drv = git_path_check_convert(ccheck + 2);
                if (ca->crlf_action != CRLF_BINARY) {
                        enum eol eol_attr = git_path_check_eol(ccheck + 3);
                        if (ca->crlf_action == CRLF_AUTO && eol_attr == EOL_LF)
                                ca->crlf_action = CRLF_AUTO_INPUT;
                        else if (ca->crlf_action == CRLF_AUTO && eol_attr == EOL_CRLF)
                                ca->crlf_action = CRLF_AUTO_CRLF;
                        else if (eol_attr == EOL_LF)
                                ca->crlf_action = CRLF_TEXT_INPUT;
                        else if (eol_attr == EOL_CRLF)
                                ca->crlf_action = CRLF_TEXT_CRLF;
                }
                ca->working_tree_encoding = git_path_check_encoding(ccheck + 5);
        } else {
                ca->drv = NULL;
                ca->crlf_action = CRLF_UNDEFINED;
                ca->ident = 0;
        }

        /* Save attr and make a decision for action */
        ca->attr_action = ca->crlf_action;
        if (ca->crlf_action == CRLF_TEXT)
                ca->crlf_action = text_eol_is_crlf() ? CRLF_TEXT_CRLF : CRLF_TEXT_INPUT;
        if (ca->crlf_action == CRLF_UNDEFINED && auto_crlf == AUTO_CRLF_FALSE)
                ca->crlf_action = CRLF_BINARY;
        if (ca->crlf_action == CRLF_UNDEFINED && auto_crlf == AUTO_CRLF_TRUE)
                ca->crlf_action = CRLF_AUTO_CRLF;
        if (ca->crlf_action == CRLF_UNDEFINED && auto_crlf == AUTO_CRLF_INPUT)
                ca->crlf_action = CRLF_AUTO_INPUT;
}

int would_convert_to_git_filter_fd(const char *path)
{
        struct conv_attrs ca;

        convert_attrs(&ca, path);
        if (!ca.drv)
                return 0;

        /*
         * Apply a filter to an fd only if the filter is required to succeed.
         * We must die if the filter fails, because the original data before
         * filtering is not available.
         */
        if (!ca.drv->required)
                return 0;

        return apply_filter(path, NULL, 0, -1, NULL, ca.drv, CAP_CLEAN, NULL);
}

const char *get_convert_attr_ascii(const char *path)
{
        struct conv_attrs ca;

        convert_attrs(&ca, path);
        switch (ca.attr_action) {
        case CRLF_UNDEFINED:
                return "";
        case CRLF_BINARY:
                return "-text";
        case CRLF_TEXT:
                return "text";
        case CRLF_TEXT_INPUT:
                return "text eol=lf";
        case CRLF_TEXT_CRLF:
                return "text eol=crlf";
        case CRLF_AUTO:
                return "text=auto";
        case CRLF_AUTO_CRLF:
                return "text=auto eol=crlf";
        case CRLF_AUTO_INPUT:
                return "text=auto eol=lf";
        }
        return "";
}

int convert_to_git(const struct index_state *istate,
                   const char *path, const char *src, size_t len,
                   struct strbuf *dst, int conv_flags)
{
        int ret = 0;
        struct conv_attrs ca;

        convert_attrs(&ca, path);

        ret |= apply_filter(path, src, len, -1, dst, ca.drv, CAP_CLEAN, NULL);
        if (!ret && ca.drv && ca.drv->required)
                die("%s: clean filter '%s' failed", path, ca.drv->name);

        if (ret && dst) {
                src = dst->buf;
                len = dst->len;
        }

        ret |= encode_to_git(path, src, len, dst, ca.working_tree_encoding, conv_flags);
        if (ret && dst) {
                src = dst->buf;
                len = dst->len;
        }

        if (!(conv_flags & CONV_EOL_KEEP_CRLF)) {
                ret |= crlf_to_git(istate, path, src, len, dst, ca.crlf_action, conv_flags);
                if (ret && dst) {
                        src = dst->buf;
                        len = dst->len;
                }
        }
        return ret | ident_to_git(path, src, len, dst, ca.ident);
}

void convert_to_git_filter_fd(const struct index_state *istate,
                              const char *path, int fd, struct strbuf *dst,
                              int conv_flags)
{
        struct conv_attrs ca;
        convert_attrs(&ca, path);

        assert(ca.drv);
        assert(ca.drv->clean || ca.drv->process);

        if (!apply_filter(path, NULL, 0, fd, dst, ca.drv, CAP_CLEAN, NULL))
                die("%s: clean filter '%s' failed", path, ca.drv->name);

        encode_to_git(path, dst->buf, dst->len, dst, ca.working_tree_encoding, conv_flags);
        crlf_to_git(istate, path, dst->buf, dst->len, dst, ca.crlf_action, conv_flags);
        ident_to_git(path, dst->buf, dst->len, dst, ca.ident);
}

static int convert_to_working_tree_internal(const char *path, const char *src,
                                            size_t len, struct strbuf *dst,
                                            int normalizing, struct delayed_checkout *dco)
{
        int ret = 0, ret_filter = 0;
        struct conv_attrs ca;

        convert_attrs(&ca, path);

        ret |= ident_to_worktree(path, src, len, dst, ca.ident);
        if (ret) {
                src = dst->buf;
                len = dst->len;
        }
        /*
         * CRLF conversion can be skipped if normalizing, unless there
         * is a smudge or process filter (even if the process filter doesn't
         * support smudge).  The filters might expect CRLFs.
         */
        if ((ca.drv && (ca.drv->smudge || ca.drv->process)) || !normalizing) {
                ret |= crlf_to_worktree(path, src, len, dst, ca.crlf_action);
                if (ret) {
                        src = dst->buf;
                        len = dst->len;
                }
        }

        ret |= encode_to_worktree(path, src, len, dst, ca.working_tree_encoding);
        if (ret) {
                src = dst->buf;
                len = dst->len;
        }

        ret_filter = apply_filter(
                path, src, len, -1, dst, ca.drv, CAP_SMUDGE, dco);
        if (!ret_filter && ca.drv && ca.drv->required)
                die("%s: smudge filter %s failed", path, ca.drv->name);

        return ret | ret_filter;
}

int async_convert_to_working_tree(const char *path, const char *src,
                                  size_t len, struct strbuf *dst,
                                  void *dco)
{
        return convert_to_working_tree_internal(path, src, len, dst, 0, dco);
}

int convert_to_working_tree(const char *path, const char *src, size_t len, struct strbuf *dst)
{
        return convert_to_working_tree_internal(path, src, len, dst, 0, NULL);
}

int renormalize_buffer(const struct index_state *istate, const char *path,
                       const char *src, size_t len, struct strbuf *dst)
{
        int ret = convert_to_working_tree_internal(path, src, len, dst, 1, NULL);
        if (ret) {
                src = dst->buf;
                len = dst->len;
        }
        return ret | convert_to_git(istate, path, src, len, dst, CONV_EOL_RENORMALIZE);
}

/*****************************************************************
 *
 * Streaming conversion support
 *
 *****************************************************************/

typedef int (*filter_fn)(struct stream_filter *,
                         const char *input, size_t *isize_p,
                         char *output, size_t *osize_p);
typedef void (*free_fn)(struct stream_filter *);

struct stream_filter_vtbl {
        filter_fn filter;
        free_fn free;
};

struct stream_filter {
        struct stream_filter_vtbl *vtbl;
};

static int null_filter_fn(struct stream_filter *filter,
                          const char *input, size_t *isize_p,
                          char *output, size_t *osize_p)
{
        size_t count;

        if (!input)
                return 0; /* we do not keep any states */
        count = *isize_p;
        if (*osize_p < count)
                count = *osize_p;
        if (count) {
                memmove(output, input, count);
                *isize_p -= count;
                *osize_p -= count;
        }
        return 0;
}

static void null_free_fn(struct stream_filter *filter)
{
        ; /* nothing -- null instances are shared */
}

static struct stream_filter_vtbl null_vtbl = {
        null_filter_fn,
        null_free_fn,
};

static struct stream_filter null_filter_singleton = {
        &null_vtbl,
};

int is_null_stream_filter(struct stream_filter *filter)
{
        return filter == &null_filter_singleton;
}


/*
 * LF-to-CRLF filter
 */

struct lf_to_crlf_filter {
        struct stream_filter filter;
        unsigned has_held:1;
        char held;
};

static int lf_to_crlf_filter_fn(struct stream_filter *filter,
                                const char *input, size_t *isize_p,
                                char *output, size_t *osize_p)
{
        size_t count, o = 0;
        struct lf_to_crlf_filter *lf_to_crlf = (struct lf_to_crlf_filter *)filter;

        /*
         * We may be holding onto the CR to see if it is followed by a
         * LF, in which case we would need to go to the main loop.
         * Otherwise, just emit it to the output stream.
         */
        if (lf_to_crlf->has_held && (lf_to_crlf->held != '\r' || !input)) {
                output[o++] = lf_to_crlf->held;
                lf_to_crlf->has_held = 0;
        }

        /* We are told to drain */
        if (!input) {
                *osize_p -= o;
                return 0;
        }

        count = *isize_p;
        if (count || lf_to_crlf->has_held) {
                size_t i;
                int was_cr = 0;

                if (lf_to_crlf->has_held) {
                        was_cr = 1;
                        lf_to_crlf->has_held = 0;
                }

                for (i = 0; o < *osize_p && i < count; i++) {
                        char ch = input[i];

                        if (ch == '\n') {
                                output[o++] = '\r';
                        } else if (was_cr) {
                                /*
                                 * Previous round saw CR and it is not followed
                                 * by a LF; emit the CR before processing the
                                 * current character.
                                 */
                                output[o++] = '\r';
                        }

                        /*
                         * We may have consumed the last output slot,
                         * in which case we need to break out of this
                         * loop; hold the current character before
                         * returning.
                         */
                        if (*osize_p <= o) {
                                lf_to_crlf->has_held = 1;
                                lf_to_crlf->held = ch;
                                continue; /* break but increment i */
                        }

                        if (ch == '\r') {
                                was_cr = 1;
                                continue;
                        }

                        was_cr = 0;
                        output[o++] = ch;
                }

                *osize_p -= o;
                *isize_p -= i;

                if (!lf_to_crlf->has_held && was_cr) {
                        lf_to_crlf->has_held = 1;
                        lf_to_crlf->held = '\r';
                }
        }
        return 0;
}

static void lf_to_crlf_free_fn(struct stream_filter *filter)
{
        free(filter);
}

static struct stream_filter_vtbl lf_to_crlf_vtbl = {
        lf_to_crlf_filter_fn,
        lf_to_crlf_free_fn,
};

static struct stream_filter *lf_to_crlf_filter(void)
{
        struct lf_to_crlf_filter *lf_to_crlf = xcalloc(1, sizeof(*lf_to_crlf));

        lf_to_crlf->filter.vtbl = &lf_to_crlf_vtbl;
        return (struct stream_filter *)lf_to_crlf;
}

/*
 * Cascade filter
 */
#define FILTER_BUFFER 1024
struct cascade_filter {
        struct stream_filter filter;
        struct stream_filter *one;
        struct stream_filter *two;
        char buf[FILTER_BUFFER];
        int end, ptr;
};

static int cascade_filter_fn(struct stream_filter *filter,
                             const char *input, size_t *isize_p,
                             char *output, size_t *osize_p)
{
        struct cascade_filter *cas = (struct cascade_filter *) filter;
        size_t filled = 0;
        size_t sz = *osize_p;
        size_t to_feed, remaining;

        /*
         * input -- (one) --> buf -- (two) --> output
         */
        while (filled < sz) {
                remaining = sz - filled;

                /* do we already have something to feed two with? */
                if (cas->ptr < cas->end) {
                        to_feed = cas->end - cas->ptr;
                        if (stream_filter(cas->two,
                                          cas->buf + cas->ptr, &to_feed,
                                          output + filled, &remaining))
                                return -1;
                        cas->ptr += (cas->end - cas->ptr) - to_feed;
                        filled = sz - remaining;
                        continue;
                }

                /* feed one from upstream and have it emit into our buffer */
                to_feed = input ? *isize_p : 0;
                if (input && !to_feed)
                        break;
                remaining = sizeof(cas->buf);
                if (stream_filter(cas->one,
                                  input, &to_feed,
                                  cas->buf, &remaining))
                        return -1;
                cas->end = sizeof(cas->buf) - remaining;
                cas->ptr = 0;
                if (input) {
                        size_t fed = *isize_p - to_feed;
                        *isize_p -= fed;
                        input += fed;
                }

                /* do we know that we drained one completely? */
                if (input || cas->end)
                        continue;

                /* tell two to drain; we have nothing more to give it */
                to_feed = 0;
                remaining = sz - filled;
                if (stream_filter(cas->two,
                                  NULL, &to_feed,
                                  output + filled, &remaining))
                        return -1;
                if (remaining == (sz - filled))
                        break; /* completely drained two */
                filled = sz - remaining;
        }
        *osize_p -= filled;
        return 0;
}

static void cascade_free_fn(struct stream_filter *filter)
{
        struct cascade_filter *cas = (struct cascade_filter *)filter;
        free_stream_filter(cas->one);
        free_stream_filter(cas->two);
        free(filter);
}

static struct stream_filter_vtbl cascade_vtbl = {
        cascade_filter_fn,
        cascade_free_fn,
};

static struct stream_filter *cascade_filter(struct stream_filter *one,
                                            struct stream_filter *two)
{
        struct cascade_filter *cascade;

        if (!one || is_null_stream_filter(one))
                return two;
        if (!two || is_null_stream_filter(two))
                return one;

        cascade = xmalloc(sizeof(*cascade));
        cascade->one = one;
        cascade->two = two;
        cascade->end = cascade->ptr = 0;
        cascade->filter.vtbl = &cascade_vtbl;
        return (struct stream_filter *)cascade;
}

/*
 * ident filter
 */
#define IDENT_DRAINING (-1)
#define IDENT_SKIPPING (-2)
struct ident_filter {
        struct stream_filter filter;
        struct strbuf left;
        int state;
        char ident[GIT_MAX_HEXSZ + 5]; /* ": x40 $" */
};

static int is_foreign_ident(const char *str)
{
        int i;

        if (!skip_prefix(str, "$Id: ", &str))
                return 0;
        for (i = 0; str[i]; i++) {
                if (isspace(str[i]) && str[i+1] != '$')
                        return 1;
        }
        return 0;
}

static void ident_drain(struct ident_filter *ident, char **output_p, size_t *osize_p)
{
        size_t to_drain = ident->left.len;

        if (*osize_p < to_drain)
                to_drain = *osize_p;
        if (to_drain) {
                memcpy(*output_p, ident->left.buf, to_drain);
                strbuf_remove(&ident->left, 0, to_drain);
                *output_p += to_drain;
                *osize_p -= to_drain;
        }
        if (!ident->left.len)
                ident->state = 0;
}

static int ident_filter_fn(struct stream_filter *filter,
                           const char *input, size_t *isize_p,
                           char *output, size_t *osize_p)
{
        struct ident_filter *ident = (struct ident_filter *)filter;
        static const char head[] = "$Id";

        if (!input) {
                /* drain upon eof */
                switch (ident->state) {
                default:
                        strbuf_add(&ident->left, head, ident->state);
                        /* fallthrough */
                case IDENT_SKIPPING:
                        /* fallthrough */
                case IDENT_DRAINING:
                        ident_drain(ident, &output, osize_p);
                }
                return 0;
        }

        while (*isize_p || (ident->state == IDENT_DRAINING)) {
                int ch;

                if (ident->state == IDENT_DRAINING) {
                        ident_drain(ident, &output, osize_p);
                        if (!*osize_p)
                                break;
                        continue;
                }

                ch = *(input++);
                (*isize_p)--;

                if (ident->state == IDENT_SKIPPING) {
                        /*
                         * Skipping until '$' or LF, but keeping them
                         * in case it is a foreign ident.
                         */
                        strbuf_addch(&ident->left, ch);
                        if (ch != '\n' && ch != '$')
                                continue;
                        if (ch == '$' && !is_foreign_ident(ident->left.buf)) {
                                strbuf_setlen(&ident->left, sizeof(head) - 1);
                                strbuf_addstr(&ident->left, ident->ident);
                        }
                        ident->state = IDENT_DRAINING;
                        continue;
                }

                if (ident->state < sizeof(head) &&
                    head[ident->state] == ch) {
                        ident->state++;
                        continue;
                }

                if (ident->state)
                        strbuf_add(&ident->left, head, ident->state);
                if (ident->state == sizeof(head) - 1) {
                        if (ch != ':' && ch != '$') {
                                strbuf_addch(&ident->left, ch);
                                ident->state = 0;
                                continue;
                        }

                        if (ch == ':') {
                                strbuf_addch(&ident->left, ch);
                                ident->state = IDENT_SKIPPING;
                        } else {
                                strbuf_addstr(&ident->left, ident->ident);
                                ident->state = IDENT_DRAINING;
                        }
                        continue;
                }

                strbuf_addch(&ident->left, ch);
                ident->state = IDENT_DRAINING;
        }
        return 0;
}

static void ident_free_fn(struct stream_filter *filter)
{
        struct ident_filter *ident = (struct ident_filter *)filter;
        strbuf_release(&ident->left);
        free(filter);
}

static struct stream_filter_vtbl ident_vtbl = {
        ident_filter_fn,
        ident_free_fn,
};

static struct stream_filter *ident_filter(const struct object_id *oid)
{
        struct ident_filter *ident = xmalloc(sizeof(*ident));

        xsnprintf(ident->ident, sizeof(ident->ident),
                  ": %s $", oid_to_hex(oid));
        strbuf_init(&ident->left, 0);
        ident->filter.vtbl = &ident_vtbl;
        ident->state = 0;
        return (struct stream_filter *)ident;
}

/*
 * Return an appropriately constructed filter for the path, or NULL if
 * the contents cannot be filtered without reading the whole thing
 * in-core.
 *
 * Note that you would be crazy to set CRLF, smuge/clean or ident to a
 * large binary blob you would want us not to slurp into the memory!
 */
struct stream_filter *get_stream_filter(const char *path, const struct object_id *oid)
{
        struct conv_attrs ca;
        struct stream_filter *filter = NULL;

        convert_attrs(&ca, path);
        if (ca.drv && (ca.drv->process || ca.drv->smudge || ca.drv->clean))
                return NULL;

        if (ca.working_tree_encoding)
                return NULL;

        if (ca.crlf_action == CRLF_AUTO || ca.crlf_action == CRLF_AUTO_CRLF)
                return NULL;

        if (ca.ident)
                filter = ident_filter(oid);

        if (output_eol(ca.crlf_action) == EOL_CRLF)
                filter = cascade_filter(filter, lf_to_crlf_filter());
        else
                filter = cascade_filter(filter, &null_filter_singleton);

        return filter;
}

void free_stream_filter(struct stream_filter *filter)
{
        filter->vtbl->free(filter);
}

int stream_filter(struct stream_filter *filter,
                  const char *input, size_t *isize_p,
                  char *output, size_t *osize_p)
{
        return filter->vtbl->filter(filter, input, isize_p, output, osize_p);
}