fix: Use min of max tokens or context length (#1322)

This PR modifies the mistralrs engine to ensure that the maximum output token length never exceeds the context length provided.

lib/engines/mistralrs/src/lib.rs

@@ -65,6 +65,7 @@ fn best_device() -> pipeline_error::Result<Device> {
 
 struct MistralRsEngine {
     mistralrs: Arc<MistralRs>,
+    context_length: usize,
 }
 
 impl MistralRsEngine {
@@ -203,6 +204,7 @@ impl MistralRsEngine {
         .with_prefix_cache_n(16);
         let engine = MistralRsEngine {
             mistralrs: builder.build(),
+            context_length: max_seq_len,
         };
 
         // skip the id used for dummy run https://github.com/EricLBuehler/mistral.rs/issues/1218
@@ -310,12 +312,21 @@ impl
             frequency_penalty: request.inner.frequency_penalty.or(det.frequency_penalty),
             presence_penalty: request.inner.presence_penalty.or(det.presence_penalty),
             stop_toks: request.inner.stop.map(to_stop_tokens).or(det.stop_toks),
-            max_len: request
+            max_len: {
+                let requested_max_tokens = request
                     .inner
                     .max_completion_tokens
                     .or(request.inner.max_tokens)
-                .map(|m| m as usize)
-                .or(det.max_len),
+                    .map(|m| m as usize);
+
+                // Ensure max_len doesn't exceed context length
+                match requested_max_tokens {
+                    Some(max_tokens) => Some(std::cmp::min(max_tokens, self.context_length)),
+                    None => det
+                        .max_len
+                        .map(|len| std::cmp::min(len, self.context_length)),
+                }
+            },
             logits_bias: request
                 .inner
                 .logit_bias
@@ -499,12 +510,17 @@ impl AsyncEngine<SingleIn<CompletionRequest>, ManyOut<Annotated<CompletionRespon
                 .clone()
                 .map(to_stop_tokens)
                 .or(det.stop_toks),
-            max_len: request
-                .inner
-                .max_tokens
-                .or(request.inner.max_tokens)
-                .map(|m| m as usize)
-                .or(det.max_len),
+            max_len: {
+                let requested_max_tokens = request.inner.max_tokens.map(|m| m as usize);
+
+                // Ensure max_len doesn't exceed context length
+                match requested_max_tokens {
+                    Some(max_tokens) => Some(std::cmp::min(max_tokens, self.context_length)),
+                    None => det
+                        .max_len
+                        .map(|len| std::cmp::min(len, self.context_length)),
+                }
+            },
             logits_bias: request
                 .inner
                 .logit_bias