From 24ac2b4c74a454fabe1b2aa1134e9551a1e32625 Mon Sep 17 00:00:00 2001
From: antirez <antirez@gmail.com>
Date: Tue, 17 Apr 2018 17:18:00 +0200
Subject: [PATCH] Streams: iterator entry deletion abilities.

---
 src/stream.h   |  2 ++
 src/t_stream.c | 51 +++++++++++++++++++++++++++++++++++++++++++++++++-
 2 files changed, 52 insertions(+), 1 deletion(-)

diff --git a/src/stream.h b/src/stream.h
index 8a019e93..61210f95 100644
--- a/src/stream.h
+++ b/src/stream.h
@@ -27,6 +27,7 @@ typedef struct stream {
  * rewriting code that also needs to iterate the stream to emit the XADD
  * commands. */
 typedef struct streamIterator {
+    stream *stream;         /* The stream we are iterating. */
     streamID master_id;     /* ID of the master entry at listpack head. */
     uint64_t master_fields_count;       /* Master entries # of fields. */
     unsigned char *master_fields_start; /* Master entries start in listpack. */
@@ -38,6 +39,7 @@ typedef struct streamIterator {
     raxIterator ri;         /* Rax iterator. */
     unsigned char *lp;      /* Current listpack. */
     unsigned char *lp_ele;  /* Current listpack cursor. */
+    unsigned char *lp_flags; /* Current entry flags pointer. */
     /* Buffers used to hold the string of lpGet() when the element is
      * integer encoded, so that there is no string representation of the
      * element inside the listpack itself. */
diff --git a/src/t_stream.c b/src/t_stream.c
index 4640f0b2..b6779a95 100644
--- a/src/t_stream.c
+++ b/src/t_stream.c
@@ -265,7 +265,7 @@ int streamAppendItem(stream *s, robj **argv, int numfields, streamID *added_id,
         /* Update count and skip the deleted fields. */
         int64_t count = lpGetInteger(lp_ele);
         lp = lpReplaceInteger(lp,&lp_ele,count+1);
-        lp_ele = lpNext(lp,lp_ele); /* seek delted. */
+        lp_ele = lpNext(lp,lp_ele); /* seek deleted. */
         lp_ele = lpNext(lp,lp_ele); /* seek master entry num fields. */
 
         /* Check if the entry we are adding, have the same fields
@@ -505,6 +505,7 @@ void streamIteratorStart(streamIterator *si, stream *s, streamID *start, streamI
             raxSeek(&si->ri,"$",NULL,0);
         }
     }
+    si->stream = s;
     si->lp = NULL; /* There is no current listpack right now. */
     si->lp_ele = NULL; /* Current listpack cursor. */
     si->rev = rev;  /* Direction, if non-zero reversed, from end to start. */
@@ -573,6 +574,7 @@ int streamIteratorGetID(streamIterator *si, streamID *id, int64_t *numfields) {
             }
 
             /* Get the flags entry. */
+            si->lp_flags = si->lp_ele;
             int flags = lpGetInteger(si->lp_ele);
             si->lp_ele = lpNext(si->lp,si->lp_ele); /* Seek ID. */
 
@@ -657,6 +659,53 @@ void streamIteratorGetField(streamIterator *si, unsigned char **fieldptr, unsign
     si->lp_ele = lpNext(si->lp,si->lp_ele);
 }
 
+/* Remove the current entry from the stream: can be called after the
+ * GetID() API or after any GetField() call, however we need to iterate
+ * a valid entry while calling this function. Moreover the function
+ * requires the entry ID we are currently iterating, that was previously
+ * returned by GetID().
+ *
+ * Note that after calling this function, next calls to GetField() can't
+ * be performed: the entry is now deleted. Instead the iterator will
+ * automatically re-seek to the next entry, so the caller should continue
+ * with GetID(). */
+void streamIteratorRemoveEntry(streamIterator *si, streamID *current) {
+    unsigned char *lp = si->lp;
+    int64_t aux;
+
+    /* We do not really delete the entry here. Instead we mark it as
+     * deleted flagging it, and also incrementing the count of the
+     * deleted entries in the listpack header.
+     *
+     * We start flagging: */
+    int flags = lpGetInteger(si->lp_flags);
+    flags |= STREAM_ITEM_FLAG_DELETED;
+    lp = lpReplaceInteger(lp,&si->lp_flags,flags);
+
+    /* Change the valid/deleted entries count in the master entry. */
+    unsigned char *p = lpFirst(lp);
+    aux = lpGetInteger(p);
+    lp = lpReplaceInteger(lp,&p,aux-1);
+    p = lpNext(lp,p); /* Seek deleted field. */
+    aux = lpGetInteger(p);
+    lp = lpReplaceInteger(lp,&p,aux+1);
+
+    /* Re-seek the iterator to fix the now messed up state. */
+    streamID start, end;
+    if (si->rev) {
+        streamDecodeID(si->start_key,&start);
+        end = *current;
+    } else {
+        start = *current;
+        streamDecodeID(si->end_key,&end);
+    }
+    streamIteratorStop(si);
+    streamIteratorStart(si,si->stream,&start,&end,si->rev);
+
+    /* TODO: perform a garbage collection here if the ration between
+     * deleted and valid goes over a certain limit. */
+}
+
 /* Stop the stream iterator. The only cleanup we need is to free the rax
  * itereator, since the stream iterator itself is supposed to be stack
  * allocated. */