19.0.0 released Nov 08, 2023
Hashed key/value server


You will create your own hash server in this example. A REST API will enable end-user to add key/data pairs, query and delete them. The data is in memory-only; a more involved example could be constructed to persist the data in some form (such as with SQLite). This is an extremely fast, single-process hash server.

In a nutshell:  web browser; Apache; REST API; Unix sockets; 2 source files, 47 lines of code.
Setup prerequisites
Install Vely - you can use standard packaging tools such as apt, dnf, pacman or zypper.

Because it is used in this example, you will need to install Apache as a web server.

After installing Vely, turn on syntax highlighting in vim if you're using it:
vv -m

Get the source code
The source code is a part of Vely installation. It is a good idea to create a separate source code directory for each application (and you can name it whatever you like). In this case, unpacking the source code will do that for you:
tar xvf $(vv -o)/examples/hash-server.tar.gz
cd hash-server

Setup application
The very first step is to create an application. The application will be named "hash-server", but you can name it anything (if you do that, change it everywhere). It's simple to do with vf:
sudo vf -i -u $(whoami) hash-server

This will create a new application home (which is "/var/lib/vv/hash-server") and do the application setup for you. Mostly that means create various subdirectories in the home folder, and assign them privileges. In this case only current user (or the result of "whoami" Linux command) will own those directories with 0700 privileges; it means a secure setup.
Build application
Use vv utility to make the application:
vv -q

Start your application server
To start the application server for your web application use vf FastCGI process manager. The application server will use a Unix socket to communicate with the web server (i.e. a reverse-proxy):
vf -w 1 hash-server

This will start 1 daemon process to serve the incoming requests.

See vf for more options to help you achieve best performance.

If you want to stop your application server:
vf -m quit hash-server

Setup web server
This shows how to connect your application listening on a Unix socket (started with vf) to Apache web server.

- Step 1:
To setup Apache as a reverse proxy and connect your application to it, you need to enable FastCGI proxy support, which generally means "proxy" and "proxy_fcgi" modules - this is done only once:
- Step 2:
Edit the Apache configuration file:
Add this to the end of file ("/hash-server" is the application path (see request-URL) and "hash-server" is your application name):
ProxyPass "/hash-server" unix:///var/lib/vv/hash-server/sock/sock|fcgi://localhost/hash-server

- Step 3:
Finally, restart Apache. On Debian systems (like Ubuntu) or OpenSUSE:
sudo systemctl restart apache2

On Fedora systems (like RedHat) and Arch Linux:
sudo systemctl restart httpd

Note: you must not have any other URL resource that starts with "/hash-server" (such as for example "/hash-server.html" or "/hash-server_something" etc.) as the web server will attempt to pass them as a reverse proxy request, and they will likely not work. If you need to, you can change the application path to be different from "/hash-server", see request-URL.

Access application server from the browser
Use the following URL(s) to access your application server from a client like browser (see request-URL). Use actual IP or web address instead of 127.0.0.1 if different.
# Add key "key_1" with data "data_1" 
http://127.0.0.1/hash-server/server/op/add/key/key_1/data/data_1

# Query key "key_1" 
http://127.0.0.1/hash-server/server/op/query/key/key_1

# Delete key "key_1" 
http://127.0.0.1/hash-server/server/op/delete/key/key_1

Note: if your server is on the Internet and it has a firewall, you may need to allow HTTP traffic - see ufw, firewall-cmd etc.

- Test hash server with a bash script
To test the hash server, you can use "test_hash" bash script (see source code):
./test_hash

This will insert 1000 key/data value pairs, query them, delete and then query again. The result is:
Keys added
Keys queried
Keys deleted
Keys queried
Hash server test successful


- Use REST API from command line
Here is the REST API for your application.

Substitute the loopback "localhost" with the IP or web address of your server.

Note that in these REST calls, the application path is "/hash-server", and the request name is "/server", followed by URL payload (see request-URL).

The request method used is based on REST methodology, i.e. POST to create resource, GET to obtain, DELETE to delete it, etc. This is how you can use the API:

Source files
The following are the source files in this application:
- Hash server (server.vely)
This is the hash server. Because the data kept in hash needs to exist beyond a single request, you'd use "process-scope" clause (see new-hash). This way hash data stays allocated and available for the life of the server process. The creation of a new hash is done within do-once statement, so it executes only once for the life of the process.

Next, you get the input parameters  (see input-param); in this case task-param "op" (operation requested), as well as "key" (value of a key) and "data" (value of data). Then, depending on the operation requested, the data is added, deleted and retrieved (i.e. queried). Note that because input parameter values are not allocated memory, they are copied into new memory before being stored in the hash; this way they survive for the life of the process - this is done automatically due to "process-scope" clause when hash was created.
%% /server
    out-header default

    do-once
    new-hash define h size 1024 process-scope
    end-do-once

    // Get input parameters
    task-param op
    input-param key
    input-param data

    if-task "add" // Add data to hash, 
        // Make a copy of input params are they are request-scoped
        copy-string key to define c_key
        copy-string data to define c_data
        write-hash h key c_key value c_data \
            old-value define old_data old-key define old_key \
            status define st
        if (st == VV_ERR_EXIST) {
            // delete old key/value if replaced by new
            delete-mem old_key
            delete-mem old_data
        }
        @Added [<<p-out key>>]
    else-task "delete" // Delete data and obtain the value deleted
        read-hash h key (key) value define val \
            old-key define okey \
            delete \
            status define st
        if (st == VV_ERR_EXIST) {
            @Not found [<<p-out key>>]
        } else {
            // If found, then delete key and value
            @Deleted [<<p-out val>>]
            delete-mem val
            delete-mem okey
        }
    else-task "query" // Query hash based on key value
        read-hash h key (key) value define val status define st
        if (st == VV_ERR_EXIST) {
            @Not found, queried [<<p-out key>>]
        } else {
            @Value [<<p-out val>>]
        }
    end-task
%%

- bash testing script (test_hash)
Test hash server by adding 1000 key/data pairs, querying to make sure the data is correct, deleting all of them and then querying to make sure they were all deleted.
#Restart hash-server server for this test
vf -m restart hash-server

#Add 1000 key/data pairs. Key value is 0,1,2... and data values are "data_0", "data_1", "data_2" etc.
for i in {1..1000}; do
    if [ "$(curl -s "http://localhost/hash-server/server/op/add/key/$i/data/data_$i")" != "Added [$i]" ]; then
        echo "Error adding key [$i]"
        exit -1
    fi
done

echo "Keys added"

#Query all 1000 keys and check that values retrieved are the correct ones.
for i in {1..1000}; do
    if [ "$(curl -s "http://localhost/hash-server/server/op/query/key/$i")" != "Value [data_$i]" ]; then
        echo "Error querying key [$i]"
        exit -1
    fi
done

echo "Keys queried"

#Delete all 1000 keys
ERR="0"
for i in {1..1000}; do
    if [ "$(curl -s "http://localhost/hash-server/server/op/delete/key/$i")" != "Deleted [data_$i]" ]; then
        echo "Error deleting key [$i]"
        exit -1
    fi
done

echo "Keys deleted"

#Query all 1000 keys and check that values retrieved are the correct ones.
for i in {1..1000}; do
    if [ "$(curl -s "http://localhost/hash-server/server/op/query/key/$i")" != "Not found, queried [$i]" ]; then
        echo "Error querying key [$i] after deletion."
        exit -1
    fi
done

echo "Keys queried"

echo "Hash server test successful"

See also
Examples
example-client-API  
example-cookies  
example-create-table  
example-develop-web-applications-in-C-programming-language  
example-distributed-servers  
example-docker  
example-encryption  
example-file-manager  
example-form  
example-hash-server  
example-hello-world  
example-how-to-design-application  
example-how-to-use-regex  
example-json  
example-multitenant-SaaS  
example-postgres-transactions  
examples  
example-sendmail  
example-shopping  
example-stock  
example-uploading-files  
example-using-mariadb-mysql  
example-using-trees-for-in-memory-queries  
example-utility  
example-write-report    
See all
documentation


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