[PATCH v7 06/45] builtin-am: auto-detect mbox patches

[Paul Tan]

Since 15ced75 (git-am foreign patch support: autodetect some patch
formats, 2009-05-27), git-am.sh is able to autodetect mbox, stgit and
mercurial patches through heuristics.

Re-implement support for autodetecting mbox/maildir files in
builtin/am.c.

RFC 2822 requires that lines are terminated by "\r\n". To support this,
implement strbuf_getline_crlf(), which will remove both '\n' and "\r\n"
from the end of the line.

Helped-by: Junio C Hamano <gits...@pobox.com>
Helped-by: Eric Sunshine <sunsh...@sunshineco.com>
Helped-by: Johannes Schindelin <johannes.schinde...@gmx.de>
Signed-off-by: Paul Tan <pyoka...@gmail.com>
---
 builtin/am.c | 109 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 109 insertions(+)

diff --git a/builtin/am.c b/builtin/am.c
index 5f3c131..c12566a 100644
--- a/builtin/am.c
+++ b/builtin/am.c
@@ -10,6 +10,21 @@
 #include "dir.h"
 #include "run-command.h"
 
+/**
+ * Like strbuf_getline(), but treats both '\n' and "\r\n" as line terminators.
+ */
+static int strbuf_getline_crlf(struct strbuf *sb, FILE *fp)
+{
+       if (strbuf_getwholeline(sb, fp, '\n'))
+               return EOF;
+       if (sb->buf[sb->len - 1] == '\n') {
+               strbuf_setlen(sb, sb->len - 1);
+               if (sb->len > 0 && sb->buf[sb->len - 1] == '\r')
+                       strbuf_setlen(sb, sb->len - 1);
+       }
+       return 0;
+}
+
 enum patch_format {
        PATCH_FORMAT_UNKNOWN = 0,
        PATCH_FORMAT_MBOX
@@ -128,6 +143,92 @@ static void am_destroy(const struct am_state *state)
 }
 
 /**
+ * Determines if the file looks like a piece of RFC2822 mail by grabbing all
+ * non-indented lines and checking if they look like they begin with valid
+ * header field names.
+ *
+ * Returns 1 if the file looks like a piece of mail, 0 otherwise.
+ */
+static int is_mail(FILE *fp)
+{
+       const char *header_regex = "^[!-9;-~]+:";
+       struct strbuf sb = STRBUF_INIT;
+       regex_t regex;
+       int ret = 1;
+
+       if (fseek(fp, 0L, SEEK_SET))
+               die_errno(_("fseek failed"));
+
+       if (regcomp(&regex, header_regex, REG_NOSUB | REG_EXTENDED))
+               die("invalid pattern: %s", header_regex);
+
+       while (!strbuf_getline_crlf(&sb, fp)) {
+               if (!sb.len)
+                       break; /* End of header */
+
+               /* Ignore indented folded lines */
+               if (*sb.buf == '\t' || *sb.buf == ' ')
+                       continue;
+
+               /* It's a header if it matches header_regex */
+               if (regexec(&regex, sb.buf, 0, NULL, 0)) {
+                       ret = 0;
+                       goto done;
+               }
+       }
+
+done:
+       regfree(&regex);
+       strbuf_release(&sb);
+       return ret;
+}
+
+/**
+ * Attempts to detect the patch_format of the patches contained in `paths`,
+ * returning the PATCH_FORMAT_* enum value. Returns PATCH_FORMAT_UNKNOWN if
+ * detection fails.
+ */
+static int detect_patch_format(const char **paths)
+{
+       enum patch_format ret = PATCH_FORMAT_UNKNOWN;
+       struct strbuf l1 = STRBUF_INIT;
+       FILE *fp;
+
+       /*
+        * We default to mbox format if input is from stdin and for directories
+        */
+       if (!*paths || !strcmp(*paths, "-") || is_directory(*paths))
+               return PATCH_FORMAT_MBOX;
+
+       /*
+        * Otherwise, check the first few lines of the first patch, starting
+        * from the first non-blank line, to try to detect its format.
+        */
+
+       fp = xfopen(*paths, "r");
+
+       while (!strbuf_getline_crlf(&l1, fp)) {
+               if (l1.len)
+                       break;
+       }
+
+       if (starts_with(l1.buf, "From ") || starts_with(l1.buf, "From: ")) {
+               ret = PATCH_FORMAT_MBOX;
+               goto done;
+       }
+
+       if (l1.len && is_mail(fp)) {
+               ret = PATCH_FORMAT_MBOX;
+               goto done;
+       }
+
+done:
+       fclose(fp);
+       strbuf_release(&l1);
+       return ret;
+}
+
+/**
  * Splits out individual email patches from `paths`, where each path is either
  * a mbox file or a Maildir. Returns 0 on success, -1 on failure.
  */
@@ -185,6 +286,14 @@ static int split_mail(struct am_state *state, enum 
patch_format patch_format,
 static void am_setup(struct am_state *state, enum patch_format patch_format,
                        const char **paths)
 {
+       if (!patch_format)
+               patch_format = detect_patch_format(paths);
+
+       if (!patch_format) {
+               fprintf_ln(stderr, _("Patch format detection failed."));
+               exit(128);
+       }
+
        if (mkdir(state->dir, 0777) < 0 && errno != EEXIST)
                die_errno(_("failed to create directory '%s'"), state->dir);
 
-- 
2.5.0.280.gd88bd6e

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