Fix tokenization of chat interfaces (#1035)

Co-authored-by: Jack-Khuu <jack.khuu.7@gmail.com>

Author: vmpuri

api/api.py

@@ -10,6 +10,8 @@
 from dataclasses import dataclass
 from typing import Any, Dict, List, Optional, Union
 
+import torch
+
 from build.utils import device_sync
 
 from generate import Generator, GeneratorArgs
@@ -222,7 +224,6 @@ def __init__(self, *args, **kwargs):
         """
 
         super().__init__(*args, **kwargs)
-        self.start_pos = 0
         self.max_seq_length = (
             self.model.config.max_seq_length
             + self.speculative_builder_args.speculate_k
@@ -257,20 +258,25 @@ def chunked_completion(self, completion_request: CompletionRequest):
             CompletionResponseChunk objects in response to completion_request as tokens are generated.
 
         """
-        device_sync(device=self.builder_args.device)
 
         # Initialize counters for chunk responses and encode the prompt.
         id = str(uuid.uuid4())
 
         idx = 0
-        buffer = []
-        encoded = self.encode_tokens(
-            completion_request.messages[-1].get("content"),
-            bos=True,
-            device=self.builder_args.device,
+        tokens = self.chat_formatter.encode_dialog_prompt(
+            dialog=[
+                {"role": message["role"], "content": message["content"]}
+                for message in completion_request.messages
+            ]
         )
+
+        encoded = torch.tensor(tokens, dtype=torch.int, device=self.builder_args.device)
+        print(self.tokenizer.decode(tokens))
+
+        start_pos = 0
+
         generator_args = GeneratorArgs(
-            completion_request.messages[-1].get("content"),
+            None,
             max_new_tokens=(
                 int(completion_request.max_tokens)
                 if completion_request.max_tokens
@@ -279,33 +285,39 @@ def chunked_completion(self, completion_request: CompletionRequest):
             encoded_prompt=encoded,
             temperature=float(completion_request.temperature),
             chat_mode=False,
+            sequential_prefill=True,
         )
 
         def callback(x, *, done_generating=False):
             return self._callback(
                 x,
-                buffer=buffer,
+                buffer=None,
                 done_generating=done_generating,
             )
 
+        device_sync(device=self.builder_args.device)
+
         # Process each token, metrics tuple yielded by Generator.generate.
         for y, _ in self.generate(
-            self.model,
-            encoded,
-            generator_args.max_new_tokens,
+            model=self.model,
+            prompt=encoded,
+            max_new_tokens=generator_args.max_new_tokens,
             draft_model=self.draft_model,
             speculate_k=generator_args.speculate_k,
             chat_mode=generator_args.chat_mode,
             callback=callback,
             temperature=generator_args.temperature,
             top_k=generator_args.top_k,
             sequential_prefill=generator_args.sequential_prefill,
-            start_pos=self.start_pos,
+            start_pos=start_pos,
             max_seq_length=self.max_seq_length,
             seed=int(completion_request.seed),
         ):
             if y is None:
                 continue
+            elif y.item() == self.tokenizer.eos_id:
+                # Stop generation if the EOS token is generated.
+                break
 
             # Decode the torch.Tensor token to a string and append to the buffer. Separate the sequences with a period token.
             content = "".join(
@@ -330,7 +342,7 @@ def callback(x, *, done_generating=False):
                 system_fingerprint=self.system_fingerprint,
             )
             yield chunk_response
-            self.start_pos += y.size(0)
+            start_pos += y.size(0)
             idx += 1
 
         # Yield an ending chunk indicating the generation has completed.
@@ -369,10 +381,4 @@ def sync_completion(self, request: CompletionRequest):
         )
 
     def _callback(self, x, *, buffer, done_generating):
-        period_id = self.tokenizer.encode(".")[0]
-        buffer.append(self.tokenizer.decode([period_id] + x.tolist())[1:])
-        if (
-            self.is_llama3_model
-            and x.item() == self.tokenizer.special_tokens["<|eot_id|>"]
-        ):
-            buffer = buffer[:-1]  # drop the eot_id from the output buffer
+        pass

generate.py

@@ -9,6 +9,8 @@
 import os
 import textwrap
 import time
+
+from abc import ABC, abstractmethod
 from dataclasses import dataclass
 from pathlib import Path
 from typing import List, Optional, Tuple
@@ -28,24 +30,33 @@
 from cli import add_arguments_for_verb, arg_init, check_args
 from utils.device_info import get_device_info
 
-B_INST, E_INST = "[INST]", "[/INST]"
-B_SYS, E_SYS = "<<SYS>>", "<</SYS>>"
-
 
-class ChatFormat:
+class _ChatFormatter(ABC):
     def __init__(self, tokenizer):
         self.tokenizer = tokenizer
 
-    def encode_header(self, message) -> List[int]:
+    @abstractmethod
+    def encode_dialog_prompt(self, dialog) -> List[int]:
+        raise NotImplementedError()
+
+
+class Llama3ChatFormatter(_ChatFormatter):
+    """Format a chat prompt using special tokens to demarcate roles and messages.
+
+    Refer to the LLaMA3 documentation for more details https://llama.meta.com/docs/model-cards-and-prompt-formats/meta-llama-3
+
+    """
+
+    def encode_header(self, role) -> List[int]:
         tokens = []
         tokens.append(self.tokenizer.special_tokens["<|start_header_id|>"])
-        tokens.extend(self.tokenizer.encode(message["role"], bos=False, eos=False))
+        tokens.extend(self.tokenizer.encode(role, bos=False, eos=False))
         tokens.append(self.tokenizer.special_tokens["<|end_header_id|>"])
         tokens.extend(self.tokenizer.encode("\n\n", bos=False, eos=False))
         return tokens
 
     def encode_message(self, message) -> List[int]:
-        tokens = self.encode_header(message)
+        tokens = self.encode_header(message.role)
         tokens.extend(
             self.tokenizer.encode(message["content"].strip(), bos=False, eos=False)
         )
@@ -62,9 +73,37 @@ def encode_dialog_prompt(self, dialog) -> List[int]:
         return tokens
 
 
+B_INST, E_INST = "[INST]", "[/INST]"
+B_SYS, E_SYS = "<<SYS>>", "<</SYS>>"
+
+
+class Llama2ChatFormatter(_ChatFormatter):
+    def encode_dialog_prompt(self, dialog) -> List[int]:
+        tokens = self.tokenizer.encode(f"{B_INST} ")
+        first_message = True  # Bool to handle placing the B_INST token. Behavior is weird - the system prompt should have the B_INST, but not the first user message. All following user messages *should* have it. Also, if there is no system prompt, then the user message should have it.
+        for message in dialog:
+            content = message["content"].strip()
+            if message["role"] == "system":
+                encoded = self.tokenizer.encode(f"{B_SYS}\n{content}\n{E_SYS}")
+                first_message = False
+            elif message["role"] == "user":
+                encoded = [self.tokenizer.bos_id()] + self.tokenizer.encode(
+                    f"{B_INST if first_message else ''} {content} {E_INST} "
+                )
+                first_message = True
+            elif message["role"] == "assistant":
+                encoded = self.tokenizer.encode(f"{content}\n\n") + [
+                    self.tokenizer.eos_id()
+                ]
+            tokens += encoded
+        return tokens
+
+
 @dataclass
 class GeneratorArgs:
-    prompt: str = "torchchat is pronounced torch-chat and is so cool because"
+    prompt: Optional[str] = (
+        None  # When passed into the Generator, this will be used as the system prompt
+    )
     encoded_prompt: Optional[torch.Tensor] = None
     chat_mode: bool = False
     gui_mode: bool = False
@@ -188,7 +227,7 @@ def __init__(
             ))
             # fmt: on
             # raise RuntimeError("You need to use --is-chat-model to indicate model has chat support.")
-
+        self.system_prompt = generator_args.prompt
         self.tokenizer = _initialize_tokenizer(self.tokenizer_args)
 
         # Right now the assumption is only llama3 uses tiktokenizer and it
@@ -200,6 +239,11 @@ def __init__(
             logging.debug(
                 "Llama3 model detected in chat mode. Using updated sentence schemas"
             )
+        self.chat_formatter = (
+            Llama3ChatFormatter(self.tokenizer)
+            if self.is_llama3_model
+            else Llama2ChatFormatter(self.tokenizer)
+        )
 
         self.builder_args.setup_caches = False
         self.model = _initialize_model(self.builder_args, self.quantize, self.tokenizer)
@@ -641,8 +685,7 @@ def chat(
             )
             if get_system_prompt == "y" or get_system_prompt == "Y":
                 self.system_prompt = input("What is your system prompt? \n")
-            if self.is_llama3_model:
-                self.chat_formatter = ChatFormat(self.tokenizer)
+
         else:
             max_seq_length = min(
                 encoded.size(0) + generator_args.max_new_tokens,
@@ -685,7 +728,7 @@ def chat(
                         prompt, bos=True, device=self.builder_args.device
                     )
                 else:
-                    if self.system_prompt is not None:
+                    if self.system_prompt:
                         encoded = self.chat_formatter.encode_dialog_prompt(
                             [
                                 {"role": "system", "content": self.system_prompt},

server.py

@@ -6,6 +6,10 @@
 
 import json
 
+import logging
+
+logger = logging.getLogger(__name__)
+
 from dataclasses import asdict
 from typing import Dict, List, Union
 
@@ -21,7 +25,7 @@
 OPENAI_API_VERSION = "v1"
 
 
-def create_app(args):
+def create_app(args):  # noqa: C901
     """
     Creates a flask app that can be used to serve the model as a chat API.
     """
@@ -69,7 +73,7 @@ def chunk_processor(chunked_completion_generator):
                 for chunk in chunked_completion_generator:
                     if (next_tok := chunk.choices[0].delta.content) is None:
                         next_tok = ""
-                    print(next_tok, end="")
+                    print(next_tok, end="", flush=True)
                     yield json.dumps(_del_none(asdict(chunk)))
 
             return Response(