More helpful error messages for missing config

synapse/config/_base.py

@@ -21,6 +21,10 @@ import os
 import yaml
 
 
+class ConfigError(Exception):
+    pass
+
+
 class Config(object):
     def __init__(self, args):
         pass
@@ -29,8 +33,25 @@ class Config(object):
     def abspath(file_path):
         return os.path.abspath(file_path) if file_path else file_path
 
-    @staticmethod
-    def read_file(file_path):
+    @classmethod
+    def check_file(cls, file_path, config_name):
+        if file_path is None:
+            raise ConfigError(
+                "Missing config for %s."
+                " Try running again with --generate-config"
+                % (config_name,)
+            )
+        if not os.path.exists(file_path):
+            raise ConfigError(
+                "File % config for %s doesn't exist."
+                " Try running again with --generate-config"
+                % (config_name,)
+            )
+        return cls.abspath(file_path)
+
+    @classmethod
+    def read_file(cls, file_path, config_name):
+        cls.check_file(file_path, config_name)
         with open(file_path) as file_stream:
             return file_stream.read()
 

synapse/config/server.py

@@ -60,7 +60,7 @@ class ServerConfig(Config):
                                   " service on the given port.")
 
     def read_signing_key(self, signing_key_path):
-        signing_key_base64 = self.read_file(signing_key_path)
+        signing_key_base64 = self.read_file(signing_key_path, "signing_key")
         signing_key_bytes = decode_base64(signing_key_base64)
         return nacl.signing.SigningKey(signing_key_bytes)
 

synapse/config/tls.py

@@ -31,7 +31,9 @@ class TlsConfig(Config):
         self.tls_private_key = self.read_tls_private_key(
             args.tls_private_key_path
         )
-        self.tls_dh_params_path = self.abspath(args.tls_dh_params_path)
+        self.tls_dh_params_path = self.check_path(
+            args.tls_dh_params_path, "tls_dh_params"
+        )
 
     @classmethod
     def add_arguments(cls, parser):
@@ -45,11 +47,11 @@ class TlsConfig(Config):
                                help="PEM dh parameters for ephemeral keys")
 
     def read_tls_certificate(self, cert_path):
-        cert_pem = self.read_file(cert_path)
+        cert_pem = self.read_file(cert_path, "tls_certificate")
         return crypto.load_certificate(crypto.FILETYPE_PEM, cert_pem)
 
     def read_tls_private_key(self, private_key_path):
-        private_key_pem = self.read_file(private_key_path)
+        private_key_pem = self.read_file(private_key_path, "tls_private_key")
         return crypto.load_privatekey(crypto.FILETYPE_PEM, private_key_pem)
 
     @classmethod