Catch requests' ConnectionError

This is a tentative fix for #44: catch exceptions raised by requests if
it cannot connect to the log so that the witness can return the
expected exit codes.

1 files changed, 12 insertions, 3 deletions

diff --git a/sigsum-witness.py b/sigsum-witness.py
index ef63c4c..5cd9f7a 100755
--- a/sigsum-witness.py
+++ b/sigsum-witness.py
@@ -279,7 +279,10 @@ def store_tree_head(tree_head):
         f.write(tree_head.text())
 
 def fetch_tree_head_and_verify(log_verification_key):
-    req = requests.get(g_args.base_url + 'sigsum/v0/get-tree-head-to-cosign')
+    try:
+        req = requests.get(g_args.base_url + 'sigsum/v0/get-tree-head-to-cosign')
+    except requests.ConnectionError as err:
+        return None, (ERR_TREEHEAD_FETCH, f"ERROR: unable to fetch new tree head: {err}")
     if req.status_code != 200:
         return None, (ERR_TREEHEAD_FETCH,
                       "ERROR: unable to fetch new tree head: {}".format(req.status_code))
@@ -293,7 +296,10 @@ def fetch_tree_head_and_verify(log_verification_key):
 
 def fetch_consistency_proof(first, second):
     url = g_args.base_url + 'sigsum/v0/get-consistency-proof/{}/{}'.format(first, second)
-    req = requests.get(url)
+    try:
+        req = requests.get(url)
+    except requests.ConnectionError as err:
+        return None, (ERR_TREEHEAD_FETCH, f"ERROR: unable to fetch consistency proof: {err}")
     if req.status_code != 200:
         return None, (ERR_CONSISTENCYPROOF_FETCH,
                       "ERROR: unable to fetch consistency proof: {}".format(req.status_code))
@@ -354,7 +360,10 @@ def sign_send_store_tree_head(signing_key, log_key, tree_head):
     post_data = 'cosignature={}\n'.format(hexlify(signature).decode('ascii'))
     post_data += 'key_hash={}\n'.format(hash.hexdigest())
 
-    req = requests.post(g_args.base_url + 'sigsum/v0/add-cosignature', post_data)
+    try:
+        req = requests.post(g_args.base_url + 'sigsum/v0/add-cosignature', post_data)
+    except requests.ConnectionError as err:
+        return (ERR_COSIG_POST, f"ERROR: Unable to post signature to log: {err}")
     if req.status_code != 200:
         return (ERR_COSIG_POST,
                 "ERROR: Unable to post signature to log: {} => {}: {}". format(req.url,