Improve the invalid 'BAM\1' magic number error message, and also print it

when no bytes can be read from the alleged BAM file, e.g., in the common
user error case when a SAM file has accidentally been supplied.

diff --git a/bam.c b/bam.c
index 56c95db4e2c42c404627e41bd1ca2360a496af73..35e5863ca4fdbe85e2ef1226773f16703f05786b 100644 (file)
--- a/bam.c
+++ b/bam.c
@@ -70,6 +70,7 @@ bam_header_t *bam_header_read(bamFile fp)
 {
        bam_header_t *header;
        char buf[4];
+       int magic_len;
        int32_t i = 1, name_len;
        // check EOF
        i = bgzf_check_EOF(fp);
@@ -80,9 +81,9 @@ bam_header_t *bam_header_read(bamFile fp)
        }
        else if (i == 0) fprintf(stderr, "[bam_header_read] EOF marker is absent.\n");
        // read "BAM1"
-       if (bam_read(fp, buf, 4) != 4) return 0;
-       if (strncmp(buf, "BAM\001", 4)) {
-               fprintf(stderr, "[bam_header_read] wrong header\n");
+       magic_len = bam_read(fp, buf, 4);
+       if (magic_len != 4 || strncmp(buf, "BAM\001", 4) != 0) {
+               fprintf(stderr, "[bam_header_read] invalid BAM binary header (this is not a BAM file).\n");
                return 0;
        }
        header = bam_header_init();