handle short writes when unzipping files

minzip fails if write() doesn't write all the data in one call.
Apparently this was good enough before, but it causes OTAs to fail all
the time now (maybe due to the recently-submitted kernel)?  Change
code to attempt continuing after short writes.

minzip/Zip.c

@@ -41,7 +41,7 @@ enum {
     CENSIZ = 20,
     CENLEN = 24,
     CENNAM = 28,
-    CENEXT = 30, 
+    CENEXT = 30,
     CENCOM = 32,
     CENDSK = 34,
     CENATT = 36,
@@ -66,13 +66,13 @@ enum {
 
     LOCSIG = 0x04034b50,      // PK34
     LOCHDR = 30,
-        
+
     LOCVER =  4,
     LOCFLG =  6,
     LOCHOW =  8,
     LOCTIM = 10,
     LOCCRC = 14,
-    LOCSIZ = 18, 
+    LOCSIZ = 18,
     LOCLEN = 22,
     LOCNAM = 26,
     LOCEXT = 28,
@@ -757,7 +757,7 @@ bool mzReadZipEntry(const ZipArchive* pArchive, const ZipEntry* pEntry,
 {
     CopyProcessArgs args;
     bool ret;
-    
+
     args.buf = buf;
     args.bufLen = bufLen;
     ret = mzProcessZipEntryContents(pArchive, pEntry, copyProcessFunction,
@@ -772,13 +772,29 @@ bool mzReadZipEntry(const ZipArchive* pArchive, const ZipEntry* pEntry,
 static bool writeProcessFunction(const unsigned char *data, int dataLen,
         void *fd)
 {
-    ssize_t n = write((int)fd, data, dataLen);
-    if (n != dataLen) {
-        LOGE("Can't write %d bytes (only %ld) from zip file: %s\n",
-                dataLen, n, strerror(errno));
-        return false;
-    }
-    return true;
+    int zeroWrites = 0;
+    ssize_t soFar = 0;
+    do {
+        ssize_t n = write((int)fd, data+soFar, dataLen-soFar);
+        if (n < 0) {
+            LOGE("Error writing %ld bytes from zip file: %s\n",
+                 dataLen-soFar, strerror(errno));
+            return false;
+        } else if (n > 0) {
+            soFar += n;
+            if (soFar == dataLen) return true;
+            if (soFar > dataLen) {
+                LOGE("write overrun?  (%ld bytes instead of %d)\n",
+                     soFar, dataLen);
+                return false;
+            }
+            zeroWrites = 0;
+        } else {
+            ++zeroWrites;
+        }
+    } while (zeroWrites < 5);
+    LOGE("too many consecutive zero-length writes\n");
+    return false;
 }
 
 /*