Updated getTLV() so it uses a fixed buffer as intermediate step

This is much more memory efficient.  Instead of decoding entire STRING from base64 to a temporary buffer or potentially very large size and then unpacking into TLV object, we decode a maximum of 48 characters at a time and unpack the resulting 36 (max) bytes until entire STRING is consumed.

getTLV() returns pack_size of final TLV, unless there is a problem with conversion, in which cae TLV is wiped and return value=0

src/HomeSpan.h

@@ -735,23 +735,39 @@ class SpanCharacteristic{
     setValFinish(notify);
   }  
 
-
   size_t getTLV(TLV8 &tlv){
+     
     if(format<FORMAT::TLV_ENC)
       return(0);
 
+    const size_t bufSize=36;                    // maximum size of buffer to store decoded bytes before unpacking into TLV; must be multiple of 3
+    TempBuffer<uint8_t> tBuf(bufSize);          // create fixed-size buffer to store decoded bytes
+    tlv.wipe();                                 // clear TLV completely
+
+    size_t nChars=strlen(value.STRING);         // total characters to decode
+    uint8_t *p=(uint8_t *)value.STRING;         // set pointer to beginning of value
+    const size_t decodeSize=bufSize/3*4;        // number of characters to decode in each pass
+    int status=0;
+    
+    while(nChars>0){
       size_t olen;
-    mbedtls_base64_decode(NULL,0,&olen,(uint8_t *)value.STRING,strlen(value.STRING));        // get length of buffer needed to decode
+      size_t n=nChars<decodeSize?nChars:decodeSize;
-    TempBuffer<uint8_t> tBuf(olen);                                                          // create temporary buffer
-
-    int ret=mbedtls_base64_decode(tBuf,olen,&olen,(uint8_t *)value.STRING,strlen(value.STRING));
       
+      int ret=mbedtls_base64_decode(tBuf,tBuf.len(),&olen,p,n);
       if(ret==MBEDTLS_ERR_BASE64_INVALID_CHARACTER){
         LOG0("\n*** WARNING:  Can't decode Characteristic::%s with getTLV().  Data is not in base-64 format\n\n",hapName);
+        tlv.wipe();
+        return(0);
+      }
+      status=tlv.unpack(tBuf,olen);
+      p+=n;
+      nChars-=n;
+    }
+    if(status>0){
+      LOG0("\n*** WARNING:  Can't unpack Characteristic::%s with getTLV().  TLV record is incomplete or corrupted\n\n",hapName);
+      tlv.wipe();
       return(0);      
     }
-
-    tlv.unpack(tBuf,olen);      
   return(tlv.pack_size());
   }
 

src/TLV8.cpp

@@ -160,7 +160,10 @@ size_t TLV8::pack(uint8_t *buf, size_t bufSize){
 
 /////////////////////////////////////
 
-void TLV8::unpack(uint8_t *buf, size_t bufSize){
+int TLV8::unpack(uint8_t *buf, size_t bufSize){
+
+  if(bufSize==0)
+    return(-1);
 
   if(empty())
     unpackPhase=0;
@@ -171,18 +174,17 @@ void TLV8::unpack(uint8_t *buf, size_t bufSize){
       case 0:
         unpackTag=*buf++;
         bufSize--;
+        add(unpackTag);
         unpackPhase=1;
         break;
 
       case 1:
         unpackBytes=*buf++;
         bufSize--;
-        if(unpackBytes==0){
+        if(unpackBytes==0)
-          add(unpackTag);
           unpackPhase=0;          
-        } else {
+        else
           unpackPhase=2;
-        }
         break;
 
       case 2:
@@ -196,6 +198,7 @@ void TLV8::unpack(uint8_t *buf, size_t bufSize){
       break;        
     }
   }
+  return(unpackPhase);
 }
 
 

src/TLV8.h

@@ -107,7 +107,7 @@ class TLV8 : public std::list<tlv8_t, Mallocator<tlv8_t>> {
   void osprint(std::ostream& os, TLV8_it it1){osprint(os, it1, it1++);}
   void osprint(std::ostream& os){osprint(os, begin(), end());}
 
-  void unpack(uint8_t *buf, size_t bufSize);
+  int unpack(uint8_t *buf, size_t bufSize);
 
   void wipe(){std::list<tlv8_t, Mallocator<tlv8_t>>().swap(*this);}
   

src/src.ino

@@ -123,7 +123,6 @@ struct HomeSpanTV : Service::Television {
 
     TLV8 orderTLV;
     
-    Serial.printf("BEFORE:\n");
     hsTV->displayOrder->getTLV(orderTLV);
     orderTLV.print();
     orderTLV.wipe();