Streams: XREAD, first draft. Handling of blocked clients still missing.

src/t_stream.c

@@ -398,10 +398,10 @@ void xlenCommand(client *c) {
  *       [RETRY <milliseconds> <ttl>] STREAMS key_1 ID_1 key_2 ID_2 ...
  *       key_N ID_N */
 void xreadCommand(client *c) {
-    long long block = 0;
+    long long timeout = 0;
     long long count = 0;
     int streams_count = 0;
-    int streams_argc = 0;
+    int streams_arg = 0;
     #define STREAMID_STATIC_VECTOR_LEN 8
     streamID static_ids[STREAMID_STATIC_VECTOR_LEN];
     streamID *ids = static_ids;
@@ -412,17 +412,17 @@ void xreadCommand(client *c) {
         char *o = c->argv[i]->ptr;
         if (!strcasecmp(o,"BLOCK") && moreargs) {
             i++;
-            if (getLongLongFromObjectOrReply(c,c->argv[i],&block,NULL) != C_OK)
-                return;
-            if (block < 0) block = 0;
+            if (getLongLongFromObjectOrReply(c,c->argv[i],&timeout,NULL)
+                != C_OK) return;
+            if (timeout < 0) timeout = 0;
         } else if (!strcasecmp(o,"COUNT") && moreargs) {
             i++;
             if (getLongLongFromObjectOrReply(c,c->argv[i],&count,NULL) != C_OK)
                 return;
             if (count < 0) count = 0;
         } else if (!strcasecmp(o,"STREAMS") && moreargs) {
-            streams_argc = i+1;
-            streams_count = (c->argc-streams_argc);
+            streams_arg = i+1;
+            streams_count = (c->argc-streams_arg);
             if ((streams_count % 2) != 0) {
                 addReplyError(c,"Unbalanced XREAD list of streams: "
                                 "for each stream key an ID or '$' must be "
@@ -438,7 +438,7 @@ void xreadCommand(client *c) {
     }
 
     /* STREAMS option is mandatory. */
-    if (streams_argc == 0) {
+    if (streams_arg == 0) {
         addReply(c,shared.syntaxerr);
         return;
     }
@@ -447,8 +447,7 @@ void xreadCommand(client *c) {
     if (streams_count > STREAMID_STATIC_VECTOR_LEN)
         ids = zmalloc(sizeof(streamID)*streams_count);
 
-    /* Try to serve the client synchronously. */
-    for (int i = streams_argc + streams_count; i < c->argc; i++) {
+    for (int i = streams_arg + streams_count; i < c->argc; i++) {
         /* Specifying "$" as last-known-id means that the client wants to be
          * served with just the messages that will arrive into the stream
          * starting from now. */
@@ -466,6 +465,43 @@ void xreadCommand(client *c) {
         if (streamParseIDOrReply(c,c->argv[i],ids+i,0) != C_OK) goto cleanup;
     }
 
+    /* Try to serve the client synchronously. */
+    for (int i = 0; i < streams_count; i++) {
+        robj *o = lookupKeyRead(c->db,c->argv[i+streams_arg]);
+        if (o == NULL) continue;
+        stream *s = o->ptr;
+        streamID *gt = ids+i; /* ID must be greater than this. */
+        if (s->last_id.ms > gt->ms ||
+            (s->last_id.ms == gt->ms && s->last_id.seq > gt->seq))
+        {
+            /* streamReplyWithRange() handles the 'start' ID as inclusive,
+             * so start from the next ID, since we want only messages with
+             * IDs greater than start. */
+            streamID start = *gt;
+            start.seq++; /* Can't overflow, it's an uint64_t */
+            streamReplyWithRange(c,s,&start,NULL,count);
+            goto cleanup;
+        }
+    }
+
+    /* Block if needed. */
+    if (timeout) {
+        /* If we are inside a MULTI/EXEC and the list is empty the only thing
+         * we can do is treating it as a timeout (even with timeout 0). */
+        if (c->flags & CLIENT_MULTI) {
+            addReply(c,shared.nullmultibulk);
+            goto cleanup;
+        }
+        blockForKeys(c, BLOCKED_STREAM, c->argv+streams_arg, streams_count,
+                     timeout, NULL, ids);
+        goto cleanup;
+    }
+
+    /* No BLOCK option, nor any stream we can serve. Reply as with a
+     * timeout happened. */
+    addReply(c,shared.nullmultibulk);
+    /* Continue to cleanup... */
+
 cleanup:
     /* Cleanup. */
     if (ids != static_ids) zfree(ids);