memblockq: implement new call pa_memblockq_peek_fixed_size()

src/pulsecore/memblockq.c

@@ -481,7 +481,6 @@ int pa_memblockq_peek(pa_memblockq* bq, pa_memchunk *chunk) {
 
     /* Do we need to spit out silence? */
     if (!bq->current_read || bq->current_read->index > bq->read_index) {
-
         size_t length;
 
         /* How much silence shall we return? */
@@ -527,6 +526,76 @@ int pa_memblockq_peek(pa_memblockq* bq, pa_memchunk *chunk) {
     return 0;
 }
 
+int pa_memblockq_peek_fixed_size(pa_memblockq *bq, size_t block_size, pa_memchunk *chunk) {
+    pa_memchunk tchunk, rchunk;
+    int64_t ri;
+    struct list_item *item;
+
+    pa_assert(bq);
+    pa_assert(block_size > 0);
+    pa_assert(chunk);
+    pa_assert(bq->silence.memblock);
+
+    if (pa_memblockq_peek(bq, &tchunk) < 0)
+        return -1;
+
+    if (tchunk.length >= block_size) {
+        *chunk = tchunk;
+        chunk->length = block_size;
+        return 0;
+    }
+
+    rchunk.memblock = pa_memblock_new(pa_memblock_get_pool(tchunk.memblock), block_size);
+    rchunk.index = 0;
+    rchunk.length = tchunk.length;
+
+    pa_memchunk_memcpy(&rchunk, &tchunk);
+    pa_memblock_unref(tchunk.memblock);
+
+    rchunk.index += tchunk.length;
+
+    /* We don't need to call fix_current_read() here, since
+     * pa_memblock_peek() already did that */
+    item = bq->current_read;
+    ri = bq->read_index + tchunk.length;
+
+    while (rchunk.index < block_size) {
+
+        if (!item || item->index > ri) {
+            /* Do we need to append silence? */
+            tchunk = bq->silence;
+
+            if (item)
+                tchunk.length = PA_MIN(tchunk.length, (size_t) (item->index - ri));
+
+        } else {
+            int64_t d;
+
+            /* We can append real data! */
+            tchunk = item->chunk;
+
+            d = ri - item->index;
+            tchunk.index += (size_t) d;
+            tchunk.length -= (size_t) d;
+
+            /* Go to next item for the next iteration */
+            item = item->next;
+        }
+
+        rchunk.length = tchunk.length = PA_MIN(tchunk.length, block_size - rchunk.index);
+        pa_memchunk_memcpy(&rchunk, &tchunk);
+
+        rchunk.index += rchunk.length;
+        ri += rchunk.length;
+    }
+
+    rchunk.index = 0;
+    rchunk.length = block_size;
+
+    *chunk = rchunk;
+    return 0;
+}
+
 void pa_memblockq_drop(pa_memblockq *bq, size_t length) {
     int64_t old;
     pa_assert(bq);

src/pulsecore/memblockq.h

@@ -95,6 +95,11 @@ void pa_memblockq_seek(pa_memblockq *bq, int64_t offset, pa_seek_mode_t seek, pa
  * was passed we return the length of the hole in chunk->length. */
 int pa_memblockq_peek(pa_memblockq* bq, pa_memchunk *chunk);
 
+/* Much like pa_memblockq_peek, but guarantees that the returned chunk
+ * will have a length of the block size passed. You must configure a
+ * silence memchunk for this memblockq if you use this call. */
+int pa_memblockq_peek_fixed_size(pa_memblockq *bq, size_t block_size, pa_memchunk *chunk);
+
 /* Drop the specified bytes from the queue. */
 void pa_memblockq_drop(pa_memblockq *bq, size_t length);
 

src/tests/memblockq-test.c

@@ -29,23 +29,43 @@
 #include <pulsecore/memblockq.h>
 #include <pulsecore/log.h>
 
+static void dump_chunk(const pa_memchunk *chunk) {
+    size_t n;
+    void *q;
+    char *e;
+
+    pa_assert(chunk);
+
+    printf("[");
+
+    q = pa_memblock_acquire(chunk->memblock);
+    for (e = (char*) q + chunk->index, n = 0; n < chunk->length; n++, e++)
+        printf("%c", *e);
+    pa_memblock_release(chunk->memblock);
+
+    printf("]");
+}
+
 static void dump(pa_memblockq *bq) {
-    printf(">");
+    pa_memchunk out;
+
+    pa_assert(bq);
+
+    /* First let's dump this as fixed block */
+    printf("FIXED >");
+    pa_memblockq_peek_fixed_size(bq, 64, &out);
+    dump_chunk(&out);
+    pa_memblock_unref(out.memblock);
+    printf("<\n");
+
+    /* Then let's dump the queue manually */
+    printf("MANUAL>");
 
     for (;;) {
-        pa_memchunk out;
-        char *e;
-        size_t n;
-        void *q;
-
         if (pa_memblockq_peek(bq, &out) < 0)
             break;
 
-        q = pa_memblock_acquire(out.memblock);
-        for (e = (char*) q + out.index, n = 0; n < out.length; n++)
-            printf("%c", *e);
-        pa_memblock_release(out.memblock);
-
+        dump_chunk(&out);
         pa_memblock_unref(out.memblock);
         pa_memblockq_drop(bq, out.length);
     }
@@ -70,7 +90,7 @@ int main(int argc, char *argv[]) {
     silence.index = 0;
     silence.length = pa_memblock_get_length(silence.memblock);
 
-    bq = pa_memblockq_new(0, 40, 10, 2, 4, 4, 40, &silence);
+    bq = pa_memblockq_new(0, 200, 10, 2, 4, 4, 40, &silence);
     assert(bq);
 
     chunk1.memblock = pa_memblock_new_fixed(p, (char*) "11", 2, 1);