msggen: add string_map type

diff --git a/contrib/msggen/msggen/gen/grpc/convert.py b/contrib/msggen/msggen/gen/grpc/convert.py
index 72178b31..3adc7978 100644
--- a/contrib/msggen/msggen/gen/grpc/convert.py
+++ b/contrib/msggen/msggen/gen/grpc/convert.py
@@ -130,6 +130,8 @@ class GrpcConverterGenerator(IGenerator):
                     "TlvStream?": f"c.{name}.map(|s| s.into())",
                     "RoutehintList?": f"c.{name}.map(|rl| rl.into())",
                     "DecodeRoutehintList?": f"c.{name}.map(|drl| drl.into())",
+                    "string_map": f"Some(c.{name})",
+                    "string_map?": f"c.{name}.unwrap_or(HashMap::new())",
                 }.get(
                     typ, f"c.{name}"  # default to just assignment
                 )
@@ -202,6 +204,7 @@ class GrpcConverterGenerator(IGenerator):
         use cln_rpc::notifications;
         use crate::pb;
         use std::str::FromStr;
+        use std::collections::HashMap;
         use bitcoin::hashes::sha256::Hash as Sha256;
         use bitcoin::hashes::Hash;
         use cln_rpc::primitives::PublicKey;
diff --git a/contrib/msggen/msggen/gen/grpc/proto.py b/contrib/msggen/msggen/gen/grpc/proto.py
index b0af147e..3f2b981a 100644
--- a/contrib/msggen/msggen/gen/grpc/proto.py
+++ b/contrib/msggen/msggen/gen/grpc/proto.py
@@ -201,7 +201,7 @@ class GrpcGenerator(IGenerator):
             if f.omit():
                 continue
 
-            opt = "optional " if f.optional else ""
+            opt = "optional " if f.optional and not (isinstance(f, PrimitiveField) and f.typename == "string_map") else ""
 
             if isinstance(f, ArrayField):
                 typename = f.override(
diff --git a/contrib/msggen/msggen/gen/grpc/unconvert.py b/contrib/msggen/msggen/gen/grpc/unconvert.py
index 974139b6..16a7591d 100644
--- a/contrib/msggen/msggen/gen/grpc/unconvert.py
+++ b/contrib/msggen/msggen/gen/grpc/unconvert.py
@@ -131,6 +131,8 @@ class GrpcUnconverterGenerator(GrpcConverterGenerator):
                     "hash?": f"c.{name}.map(|v| Sha256::from_slice(&v).unwrap())",
                     "txid": f"hex::encode(&c.{name})",
                     "TlvStream?": f"c.{name}.map(|s| s.into())",
+                    "string_map": f"c.{name}.unwrap()",
+                    "string_map?": f"Some(c.{name})",
                 }.get(
                     typ, f"c.{name}"  # default to just assignment
                 )
diff --git a/contrib/msggen/msggen/gen/grpc/util.py b/contrib/msggen/msggen/gen/grpc/util.py
index 2682d96b..267691d5 100644
--- a/contrib/msggen/msggen/gen/grpc/util.py
+++ b/contrib/msggen/msggen/gen/grpc/util.py
@@ -35,6 +35,7 @@ typemap = {
     "secret": "bytes",
     "bip340sig": "string",
     "hash": "bytes",
+    "string_map": "map<string, string>",
 }
 
 
diff --git a/contrib/msggen/msggen/gen/rpc/rust.py b/contrib/msggen/msggen/gen/rpc/rust.py
index 14beeae6..b2fa7625 100644
--- a/contrib/msggen/msggen/gen/rpc/rust.py
+++ b/contrib/msggen/msggen/gen/rpc/rust.py
@@ -46,6 +46,7 @@ typemap = {
     "secret": "Secret",
     "bip340sig": "String",
     "integer": "i64",
+    "string_map": "HashMap<String, String>",
 }
 
 header = f"""
@@ -306,6 +307,7 @@ class RustGenerator(IGenerator):
             #[allow(unused_imports)]
             use serde::{{Deserialize, Serialize}};
             use core::fmt::Debug;
+            use std::collections::HashMap;
             use super::{IntoRequest, Request, TypedRequest};
         """
         )
diff --git a/contrib/msggen/msggen/model.py b/contrib/msggen/msggen/model.py
index 50317abe..21b99d51 100644
--- a/contrib/msggen/msggen/model.py
+++ b/contrib/msggen/msggen/model.py
@@ -432,6 +432,7 @@ class PrimitiveField(Field):
         "secret",
         "bip340sig",
         "hash",
+        "string_map",
     ]
 
     def __init__(self, typename, path, description, added, deprecated):
diff --git a/contrib/pyln-testing/pyln/testing/fixtures.py b/contrib/pyln-testing/pyln/testing/fixtures.py
index ef55ecd0..5a439677 100644
--- a/contrib/pyln-testing/pyln/testing/fixtures.py
+++ b/contrib/pyln-testing/pyln/testing/fixtures.py
@@ -411,6 +411,17 @@ def _extra_validator(is_request: bool):
             return True
         return False
 
+    def is_string_map(checker, instance):
+        """key, value map with strings"""
+        if not checker.is_type(instance, "object"):
+            return False
+        for k, v in instance.items():
+            if not checker.is_type(k, "string"):
+                return False
+            if not checker.is_type(v, "string"):
+                return False
+        return True
+
     # "msat" for request can be many forms
     if is_request:
         is_msat = is_msat_request
@@ -439,6 +450,7 @@ def _extra_validator(is_request: bool):
         "outpoint": is_outpoint,
         "feerate": is_feerate,
         "outputdesc": is_outputdesc,
+        "string_map": is_string_map,
     })
 
     return jsonschema.validators.extend(jsonschema.Draft7Validator,