Blob binding inout direction does not seem to be supported

[AharonDror]

I've been using azure function with a binding:
{ "name": "someName", "type": "blob", "direction": "out", "path": "some/path.json", "connection": "<storage>" }
This worked just fine, until recently I needed to use the same blob that was written in the function's last execution as an input for my function. I changed the direction of the binding to "inout" as stated in the docs: https://docs.microsoft.com/en-us/azure/azure-functions/functions-bindings-storage-blob

This did not work. The function throws an error:

Cannot bind blob to Stream using FileAccess ReadWrite

When I opened the 'Integrate' tab of the function I couldn't see the input/out for that binding.
The workaround of defining 2 bindings, one with an out direction and one with an in direction with different names but the same path + connection worked for me, but is obviously less convenient and not consistent with the docs.

[Paqi]

I've encountered this problem with a Powershell script Azure Function, but had no problem with a C# Azure Function.

[paulbatum]

@AharonDror can you give us your function signature?

[pankajarm]

@paulbatum I have this same issue with python azure function. I am pretty sure, i am missing right docs on this but couldn't find anything related in existing docs, https://docs.microsoft.com/en-us/azure/azure-functions/functions-bindings-storage-blob)
Workaround of defining two bindings, one with an out and another in direction connection worked, however as @AharonDror reported, this is obviously not convenient and for me could lead to a bad design scenarios.
Here is the function signature, I am using.
{
"bindings": [
{
"authLevel": "function",
"type": "httpTrigger",
"direction": "in",
"name": "req",
"methods": [
"post"
]
},
{
"type": "http",
"direction": "out",
"name": "res"
},
{
"type": "blob",
"name": "appendoutput",
"path": "blob_name/file.txt",
"direction": "inout",
"connection": "azure_STORAGE"
}
],
"disabled": false
}

Any advise, would be appreciated.

[paulbatum]

By function signature, I meant the method signature. e.g. the definition of the function including return type and params.

[pankajarm]

Ohh.. Sure, Here is complete function, nothing fancy...

import os
import json
import logging


logging.basicConfig(filename='custom.log',level=logging.DEBUG)

postreqdata = json.loads(open(os.environ['req']).read())
response = open(os.environ['res'], 'w')

new_row = "some data string"

try:
    response.write("Event Added => " + new_row)
    response.close()
except Exception as e:
    logging.warning(e)

# Read inputfile given from ENV variable named 'readinput'
try:
    input_file = open(os.environ['readinput'], 'r')
    read_text = input_file.read()
    input_file.close()
except Exception as e:
    logging.warning(e)

# appended_text
if read_text:
    appended_text = read_text + '\n'+ new_row
else:
    appended_text = new_row

# Encrypt text with ROT13 encryption
encrypted_text= appended_text.decode('rot13')

# Write new row to existing input file given from ENV variable named 'appendoutput'
try:
    output_file = open(os.environ['appendoutput'], 'a')
    output_file.write(encrypted_text)
    output_file.close()
except Exception as e:
    logging.warning(e)

# Run Ends here

[paulbatum]

Ahh of course, I somehow missed that you were talking about python and did not make the connection. Short version - its not supported yet. This is tracked by: #49

Closing this one as a duplicate.