From eb845c094f057669e949659beb14b49e3a5c96c7 Mon Sep 17 00:00:00 2001
From: Andrea Marchesini <amarchesini@mozilla.com>
Date: Wed, 29 Jul 2020 10:52:30 +0000
Subject: [xpcom] Make Base64 compatible with ReadSegments() with small
 buffers.

---
 xpcom/io/Base64.cpp | 32 +++++++++++++++++++++++++-------
 1 file changed, 25 insertions(+), 7 deletions(-)

(limited to 'xpcom')

diff --git a/xpcom/io/Base64.cpp b/xpcom/io/Base64.cpp
index 911c0595ac..b9fa7baf83 100644
--- a/xpcom/io/Base64.cpp
+++ b/xpcom/io/Base64.cpp
@@ -108,30 +108,51 @@ EncodeInputStream_Encoder(nsIInputStream* aStream,
   EncodeInputStream_State<T>* state =
     static_cast<EncodeInputStream_State<T>*>(aClosure);
 
+  // We always consume all data.
+  *aWriteCount = aCount;
+
   // If we have any data left from last time, encode it now.
   uint32_t countRemaining = aCount;
   const unsigned char* src = (const unsigned char*)aFromSegment;
   if (state->charsOnStack) {
+    MOZ_ASSERT(state->charsOnStack == 1 || state->charsOnStack == 2);
+
+    // Not enough data to compose a triple.
+    if (state->charsOnStack == 1 && countRemaining == 1) {
+      state->charsOnStack = 2;
+      state->c[1] = src[0];
+      return NS_OK;
+    }
+
+    uint32_t consumed = 0;
     unsigned char firstSet[4];
     if (state->charsOnStack == 1) {
       firstSet[0] = state->c[0];
       firstSet[1] = src[0];
-      firstSet[2] = (countRemaining > 1) ? src[1] : '\0';
+      firstSet[2] = src[1];
       firstSet[3] = '\0';
+      consumed = 2;
     } else /* state->charsOnStack == 2 */ {
       firstSet[0] = state->c[0];
       firstSet[1] = state->c[1];
       firstSet[2] = src[0];
       firstSet[3] = '\0';
+      consumed = 1;
     }
+
     Encode(firstSet, 3, state->buffer);
     state->buffer += 4;
-    countRemaining -= (3 - state->charsOnStack);
-    src += (3 - state->charsOnStack);
+    countRemaining -= consumed;
+    src += consumed;
     state->charsOnStack = 0;
+
+    // Bail if there is nothing left.
+    if (!countRemaining) {
+      return NS_OK;
+    }
   }
 
-  // Encode the bulk of the
+  // Encode as many full triplets as possible.
   uint32_t encodeLength = countRemaining - countRemaining % 3;
   MOZ_ASSERT(encodeLength % 3 == 0,
              "Should have an exact number of triplets!");
@@ -140,9 +161,6 @@ EncodeInputStream_Encoder(nsIInputStream* aStream,
   src += encodeLength;
   countRemaining -= encodeLength;
 
-  // We must consume all data, so if there's some data left stash it
-  *aWriteCount = aCount;
-
   if (countRemaining) {
     // We should never have a full triplet left at this point.
     MOZ_ASSERT(countRemaining < 3, "We should have encoded more!");
-- 
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