4 files changed, 100 insertions, 21 deletions
diff --git a/app/scripts/lib/createErrorMiddleware.js b/app/scripts/lib/createErrorMiddleware.js
new file mode 100644
index 000000000..baed99e45
--- /dev/null
+++ b/app/scripts/lib/createErrorMiddleware.js
@@ -0,0 +1,66 @@
+const log = require('loglevel')
+
+/**
+ * JSON-RPC error object
+ *
+ * @typedef {Object} RpcError
+ * @property {number} code - Indicates the error type that occurred
+ * @property {Object} [data] - Contains additional information about the error
+ * @property {string} [message] - Short description of the error
+ */
+
+/**
+ * Middleware configuration object
+ *
+ * @typedef {Object} MiddlewareConfig
+ * @property {boolean} [override] - Use RPC_ERRORS message in place of provider message
+ */
+
+/**
+ * Map of standard and non-standard RPC error codes to messages
+ */
+const RPC_ERRORS = {
+  1: 'An unauthorized action was attempted.',
+  2: 'A disallowed action was attempted.',
+  3: 'An execution error occurred.',
+  [-32600]: 'The JSON sent is not a valid Request object.',
+  [-32601]: 'The method does not exist / is not available.',
+  [-32602]: 'Invalid method parameter(s).',
+  [-32603]: 'Internal JSON-RPC error.',
+  [-32700]: 'Invalid JSON was received by the server. An error occurred on the server while parsing the JSON text.',
+  internal: 'Internal server error.',
+  unknown: 'Unknown JSON-RPC error.',
+}
+
+/**
+ * Modifies a JSON-RPC error object in-place to add a human-readable message,
+ * optionally overriding any provider-supplied message
+ *
+ * @param {RpcError} error - JSON-RPC error object
+ * @param {boolean} override - Use RPC_ERRORS message in place of provider message
+ */
+function sanitizeRPCError (error, override) {
+  if (error.message && !override) { return error }
+  const message = error.code > -31099 && error.code < -32100 ? RPC_ERRORS.internal : RPC_ERRORS[error.code]
+  error.message = message || RPC_ERRORS.unknown
+}
+
+/**
+ * json-rpc-engine middleware that both logs standard and non-standard error
+ * messages and ends middleware stack traversal if an error is encountered
+ *
+ * @param {MiddlewareConfig} [config={override:true}] - Middleware configuration
+ * @returns {Function} json-rpc-engine middleware function
+ */
+function createErrorMiddleware ({ override = true } = {}) {
+  return (req, res, next) => {
+    next(done => {
+      const { error } = res
+      if (!error) { return done() }
+      sanitizeRPCError(error)
+      log.error(`MetaMask - RPC Error: ${error.message}`, error)
+    })
+  }
+}
+
+module.exports = createErrorMiddleware
+\ No newline at end of file
diff --git a/app/scripts/lib/get-first-preferred-lang-code.js b/app/scripts/lib/get-first-preferred-lang-code.js
index 5473fccf0..1e6a83ba6 100644
--- a/app/scripts/lib/get-first-preferred-lang-code.js
+++ b/app/scripts/lib/get-first-preferred-lang-code.js
@@ -2,6 +2,12 @@ const extension = require('extensionizer')
 const promisify = require('pify')
 const allLocales = require('../../_locales/index.json')
 
+const isSupported = extension.i18n && extension.i18n.getAcceptLanguages
+const getPreferredLocales = isSupported ? promisify(
+  extension.i18n.getAcceptLanguages,
+  { errorFirst: false }
+) : async () => []
+
 const existingLocaleCodes = allLocales.map(locale => locale.code.toLowerCase().replace('_', '-'))
 
 /**
@@ -12,10 +18,7 @@ const existingLocaleCodes = allLocales.map(locale => locale.code.toLowerCase().r
  *
  */
 async function getFirstPreferredLangCode () {
-  const userPreferredLocaleCodes = await promisify(
-    extension.i18n.getAcceptLanguages,
-    { errorFirst: false }
-  )()
+  const userPreferredLocaleCodes = await getPreferredLocales()
   const firstPreferredLangCode = userPreferredLocaleCodes
     .map(code => code.toLowerCase())
     .find(code => existingLocaleCodes.includes(code))
diff --git a/app/scripts/lib/inpage-provider.js b/app/scripts/lib/inpage-provider.js
index 99cc5d2cf..4e65f0a23 100644
--- a/app/scripts/lib/inpage-provider.js
+++ b/app/scripts/lib/inpage-provider.js
@@ -1,5 +1,6 @@
 const pump = require('pump')
 const RpcEngine = require('json-rpc-engine')
+const createErrorMiddleware = require('./createErrorMiddleware')
 const createIdRemapMiddleware = require('json-rpc-engine/src/idRemapMiddleware')
 const createStreamMiddleware = require('json-rpc-middleware-stream')
 const LocalStorageStore = require('obs-store')
@@ -44,6 +45,7 @@ function MetamaskInpageProvider (connectionStream) {
   // handle sendAsync requests via dapp-side rpc engine
   const rpcEngine = new RpcEngine()
   rpcEngine.push(createIdRemapMiddleware())
+  rpcEngine.push(createErrorMiddleware())
   rpcEngine.push(streamMiddleware)
   self.rpcEngine = rpcEngine
 }
diff --git a/app/scripts/lib/setupRaven.js b/app/scripts/lib/setupRaven.js
index b1b67f771..d164827ab 100644
--- a/app/scripts/lib/setupRaven.js
+++ b/app/scripts/lib/setupRaven.js
@@ -25,7 +25,7 @@ function setupRaven(opts) {
       const report = opts.data
       try {
         // handle error-like non-error exceptions
-        nonErrorException(report)
+        rewriteErrorLikeExceptions(report)
         // simplify certain complex error messages (e.g. Ethjs)
         simplifyErrorMessages(report)
         // modify report urls
@@ -42,27 +42,35 @@ function setupRaven(opts) {
   return Raven
 }
 
-function nonErrorException(report) {
-  // handle errors that lost their error-ness in serialization
-  if (report.message.includes('Non-Error exception captured with keys: message')) {
-    if (!(report.extra && report.extra.__serialized__)) return
-    report.message = `Non-Error Exception: ${report.extra.__serialized__.message}`
-  }
+function rewriteErrorLikeExceptions(report) {
+  // handle errors that lost their error-ness in serialization (e.g. dnode)
+  rewriteErrorMessages(report, (errorMessage) => {
+    if (!errorMessage.includes('Non-Error exception captured with keys:')) return errorMessage
+    if (!(report.extra && report.extra.__serialized__ && report.extra.__serialized__.message)) return errorMessage
+    return `Non-Error Exception: ${report.extra.__serialized__.message}`
+  })
 }
 
 function simplifyErrorMessages(report) {
+  rewriteErrorMessages(report, (errorMessage) => {
+    // simplify ethjs error messages
+    errorMessage = extractEthjsErrorMessage(errorMessage)
+    // simplify 'Transaction Failed: known transaction'
+    if (errorMessage.indexOf('Transaction Failed: known transaction') === 0) {
+      // cut the hash from the error message
+      errorMessage = 'Transaction Failed: known transaction'
+    }
+    return errorMessage
+  })
+}
+
+function rewriteErrorMessages(report, rewriteFn) {
+  // rewrite top level message
+  report.message = rewriteFn(report.message)
+  // rewrite each exception message
   if (report.exception && report.exception.values) {
     report.exception.values.forEach(item => {
-      let errorMessage = item.value
-      // simplify ethjs error messages
-      errorMessage = extractEthjsErrorMessage(errorMessage)
-      // simplify 'Transaction Failed: known transaction'
-      if (errorMessage.indexOf('Transaction Failed: known transaction') === 0) {
-        // cut the hash from the error message
-        errorMessage = 'Transaction Failed: known transaction'
-      }
-      // finalize
-      item.value = errorMessage
+      item.value = rewriteFn(item.value)
     })
   }
 }