Converting Genesys Cloud Telephony API Fax Streams to PDF via Rust

What You Will Build

You will build a Rust service that queries Genesys Cloud fax records, validates page constraints and protocol status, triggers atomic PDF conversion via the Telephony API, processes conversion webhook events, and generates structured audit logs for compliance tracking.
This implementation uses the Genesys Cloud Telephony Fax API and the reqwest HTTP client library.
The programming language covered is Rust with async/await patterns using tokio.

Prerequisites

• OAuth2 Client Credentials grant type with scopes: telephony:fax:read, telephony:fax:write
• Genesys Cloud API version v2
• Rust 1.75+ with tokio, reqwest, serde, chrono, tracing, uuid, serde_json, std::time
• External dependencies: reqwest = { version = "0.11", features = ["json", "stream"] }, serde = { version = "1.0", features = ["derive"] }, tokio = { version = "1", features = ["full"] }, chrono = { version = "0.4", features = ["serde"] }, tracing = "0.1", uuid = { version = "1", features = ["v4"] }, serde_json = "1.0"

Authentication Setup

Genesys Cloud uses OAuth2 client credentials for server-to-server integration. The token expires after 3600 seconds. Production code must cache the token and refresh it before expiration to avoid 401 interruptions during conversion batches.

use reqwest::Client;
use serde::{Deserialize, Serialize};
use std::sync::Arc;
use tokio::sync::Mutex;
use chrono::Utc;

#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct OAuthToken {
    pub access_token: String,
    pub token_type: String,
    pub expires_in: u64,
}

pub struct TokenCache {
    client: Client,
    base_url: String,
    client_id: String,
    client_secret: String,
    token: Mutex<Option<OAuthToken>>,
    expires_at: Mutex<Option<chrono::DateTime<Utc>>>,
}

impl TokenCache {
    pub fn new(base_url: &str, client_id: &str, client_secret: &str) -> Self {
        Self {
            client: Client::new(),
            base_url: base_url.to_string(),
            client_id: client_id.to_string(),
            client_secret: client_secret.to_string(),
            token: Mutex::new(None),
            expires_at: Mutex::new(None),
        }
    }

    pub async fn get_access_token(&self) -> Result<String, reqwest::Error> {
        let mut expires = self.expires_at.lock().await;
        if let Some(exp) = *expires {
            if exp > Utc::now() {
                drop(expires);
                let tok = self.token.lock().await;
                return Ok(tok.as_ref().unwrap().access_token.clone());
            }
        }
        drop(expires);

        let resp = self.client
            .post(format!("{}/oauth/token", self.base_url))
            .form(&[
                ("grant_type", "client_credentials"),
                ("client_id", &self.client_id),
                ("client_secret", &self.client_secret),
            ])
            .send()
            .await?;

        if !resp.status().is_success() {
            let status = resp.status();
            let body = resp.text().await.unwrap_or_default();
            return Err(reqwest::Error::from(std::io::Error::new(
                std::io::ErrorKind::Other,
                format!("OAuth failure {}: {}", status, body)
            )));
        }

        let token: OAuthToken = resp.json().await?;
        let now = Utc::now();
        let expires = now + chrono::Duration::seconds(token.expires_in as i64 - 30);

        let mut tok = self.token.lock().await;
        *tok = Some(token.clone());
        let mut exp = self.expires_at.lock().await;
        *exp = Some(expires);
        
        Ok(token.access_token)
    }
}

The cache checks expiration with a 30-second buffer. This prevents edge-case 401 errors during high-throughput conversion loops. The token_type field is typically Bearer.

Implementation

Step 1: Fax Validation and Payload Construction

The Genesys Cloud fax engine enforces strict constraints before conversion. You must verify the fax status, protocol, and page count. The Telephony API rejects requests for incomplete faxes, unsupported protocols, or payloads exceeding the organizational page limit.

use serde::{Deserialize, Serialize};
use tracing::info;

#[derive(Debug, Deserialize)]
pub struct FaxRecord {
    pub id: String,
    pub status: String,
    pub protocol: String,
    pub page_count: Option<u32>,
    pub direction: String,
}

pub struct FaxValidator {
    max_pages: u32,
    allowed_statuses: Vec<String>,
}

impl FaxValidator {
    pub fn new(max_pages: u32) -> Self {
        Self {
            max_pages,
            allowed_statuses: vec!["delivered".to_string(), "completed".to_string()],
        }
    }

    pub fn validate(&self, fax: &FaxRecord) -> Result<(), String> {
        if !self.allowed_statuses.contains(&fax.status) {
            return Err(format!("Fax status {} is not ready for conversion", fax.status));
        }

        if !matches!(fax.protocol.as_str(), "T.38" | "T.30" | "G.711") {
            return Err(format!("Unsupported protocol {} for PDF conversion", fax.protocol));
        }

        if let Some(pages) = fax.page_count {
            if pages == 0 || pages > self.max_pages {
                return Err(format!("Page count {} exceeds engine limit of {}", pages, self.max_pages));
            }
        }

        info!(fax_id = fax.id, pages = fax.page_count, "Validation passed for conversion");
        Ok(())
    }
}

#[derive(Debug, Serialize)]
pub struct ConvertPayload {
    pub fax_id: String,
}

The validator checks three constraints: status readiness, protocol compatibility, and page matrix limits. T.38 decoding is handled server-side by Genesys Cloud. The Rust layer only verifies that the protocol field indicates a decodable format. The ConvertPayload matches the exact schema expected by the POST /api/v2/telephony/fax/convert endpoint.

Step 2: Atomic Conversion POST and PDF Assembly

The conversion endpoint returns a binary PDF stream. You must handle the response as a byte array, verify the content type, and implement retry logic for 429 rate limits. The API uses an atomic POST operation. If the fax is locked or being processed, the engine returns 409.

use reqwest::StatusCode;
use std::time::Instant;

pub struct FaxConverter {
    client: Client,
    base_url: String,
    token_cache: Arc<TokenCache>,
}

impl FaxConverter {
    pub fn new(base_url: &str, token_cache: Arc<TokenCache>) -> Self {
        Self {
            client: Client::builder()
                .timeout(std::time::Duration::from_secs(30))
                .build()
                .unwrap(),
            base_url: base_url.to_string(),
            token_cache,
        }
    }

    pub async fn convert_fax(&self, payload: &ConvertPayload) -> Result<Vec<u8>, Box<dyn std::error::Error>> {
        let start = Instant::now();
        let token = self.token_cache.get_access_token().await?;
        
        let url = format!("{}/api/v2/telephony/fax/convert", self.base_url);
        
        let mut attempt = 0;
        let max_retries = 3;
        let mut last_err = None;

        while attempt < max_retries {
            let resp = self.client
                .post(&url)
                .header("Authorization", format!("Bearer {}", token))
                .header("Content-Type", "application/json")
                .json(payload)
                .send()
                .await?;

            match resp.status() {
                StatusCode::OK => {
                    let content_type = resp.headers().get("Content-Type")
                        .and_then(|v| v.to_str().ok())
                        .unwrap_or("");
                    
                    if !content_type.contains("application/pdf") {
                        return Err(format!("Unexpected content type: {}", content_type).into());
                    }

                    let pdf_bytes = resp.bytes().await?.to_vec();
                    let latency_ms = start.elapsed().as_millis();
                    info!(fax_id = payload.fax_id, latency_ms, "PDF conversion successful");
                    return Ok(pdf_bytes);
                }
                StatusCode::TOO_MANY_REQUESTS => {
                    attempt += 1;
                    let wait = std::time::Duration::from_secs(2u64.pow(attempt));
                    tokio::time::sleep(wait).await;
                    last_err = Some("Rate limited".to_string());
                }
                StatusCode::CONFLICT => {
                    return Err("Fax is locked or currently processing".into());
                }
                StatusCode::UNAUTHORIZED | StatusCode::FORBIDDEN => {
                    return Err(format!("Auth failure: {}", resp.status()).into());
                }
                _ => {
                    let body = resp.text().await.unwrap_or_default();
                    return Err(format!("API error {}: {}", resp.status(), body).into());
                }
            }
        }

        Err(format!("Max retries exceeded. Last error: {}", last_err.unwrap_or_default()).into())
    }
}

The retry loop handles 429 responses with exponential backoff. The content-type verification ensures the response is a valid PDF stream before assembly. Latency tracking captures the full request cycle for performance auditing.

Step 3: Webhook Synchronization and Audit Logging

Genesys Cloud emits a telephony:fax:converted webhook when conversion completes asynchronously or when batch processing finishes. You must parse the event payload, extract the fax ID, and synchronize with external document stores. Audit logs capture conversion status, page count, latency, and OCR confidence metrics if available.

use serde::Deserialize;
use chrono::Utc;
use uuid::Uuid;

#[derive(Debug, Deserialize)]
pub struct FaxWebhookEvent {
    pub event_type: String,
    pub data: WebhookData,
}

#[derive(Debug, Deserialize)]
pub struct WebhookData {
    pub fax_id: String,
    pub status: String,
    pub page_count: Option<u32>,
    pub pdf_url: Option<String>,
    pub ocr_confidence: Option<f32>,
}

#[derive(Debug, Serialize)]
pub struct AuditLogEntry {
    pub audit_id: String,
    pub timestamp: String,
    pub fax_id: String,
    pub action: String,
    pub status: String,
    pub latency_ms: u128,
    pub page_count: Option<u32>,
    pub ocr_confidence: Option<f32>,
}

pub struct FaxWebhookHandler {
    logger: Arc<Mutex<Vec<AuditLogEntry>>>,
}

impl FaxWebhookHandler {
    pub fn new() -> Self {
        Self {
            logger: Arc::new(Mutex::new(Vec::new())),
        }
    }

    pub async fn process_event(&self, event: &FaxWebhookEvent) -> Result<(), String> {
        if event.event_type != "telephony:fax:converted" {
            return Ok(());
        }

        let data = &event.data;
        let audit = AuditLogEntry {
            audit_id: Uuid::new_v4().to_string(),
            timestamp: Utc::now().to_rfc3339(),
            fax_id: data.fax_id.clone(),
            action: "CONVERT".to_string(),
            status: data.status.clone(),
            latency_ms: 0,
            page_count: data.page_count,
            ocr_confidence: data.ocr_confidence,
        };

        if let Some(conf) = data.ocr_confidence {
            if conf < 0.75 {
                tracing::warn!(fax_id = data.fax_id, confidence = conf, "Low OCR confidence detected");
            }
        }

        let mut logs = self.logger.lock().await;
        logs.push(audit);
        
        info!(fax_id = data.fax_id, "Webhook event processed and audit logged");
        Ok(())
    }

    pub async fn get_success_rate(&self) -> f32 {
        let logs = self.logger.lock().await;
        let total = logs.len() as f32;
        if total == 0.0 {
            return 0.0;
        }
        let success = logs.iter().filter(|l| l.status == "success" || l.status == "completed").count() as f32;
        success / total
    }
}

The webhook handler filters for the correct event type, validates OCR confidence thresholds, and appends structured audit entries. The success rate calculation provides real-time conversion efficiency metrics. External document store synchronization would occur within the process_event method by pushing the pdf_url or byte payload to S3, Azure Blob, or an on-premise archive.

Complete Working Example

The following module integrates authentication, validation, conversion, webhook handling, and audit logging into a single runnable service. Replace the placeholder credentials with valid Genesys Cloud OAuth values.

use reqwest::Client;
use serde::{Deserialize, Serialize};
use std::sync::Arc;
use tokio::sync::Mutex;
use chrono::Utc;
use tracing::{info, error};
use uuid::Uuid;
use std::time::Instant;

#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct OAuthToken {
    pub access_token: String,
    pub expires_in: u64,
}

pub struct TokenCache {
    client: Client,
    base_url: String,
    client_id: String,
    client_secret: String,
    token: Mutex<Option<OAuthToken>>,
    expires_at: Mutex<Option<chrono::DateTime<Utc>>>,
}

impl TokenCache {
    pub fn new(base_url: &str, client_id: &str, client_secret: &str) -> Self {
        Self {
            client: Client::new(),
            base_url: base_url.to_string(),
            client_id: client_id.to_string(),
            client_secret: client_secret.to_string(),
            token: Mutex::new(None),
            expires_at: Mutex::new(None),
        }
    }

    pub async fn get_access_token(&self) -> Result<String, reqwest::Error> {
        let mut expires = self.expires_at.lock().await;
        if let Some(exp) = *expires {
            if exp > Utc::now() {
                drop(expires);
                let tok = self.token.lock().await;
                return Ok(tok.as_ref().unwrap().access_token.clone());
            }
        }
        drop(expires);

        let resp = self.client
            .post(format!("{}/oauth/token", self.base_url))
            .form(&[("grant_type", "client_credentials"), ("client_id", &self.client_id), ("client_secret", &self.client_secret)])
            .send().await?;

        if !resp.status().is_success() {
            return Err(reqwest::Error::from(std::io::Error::new(std::io::ErrorKind::Other, format!("OAuth error: {}", resp.status()))));
        }

        let token: OAuthToken = resp.json().await?;
        let now = Utc::now();
        let expires = now + chrono::Duration::seconds(token.expires_in as i64 - 30);
        let mut tok = self.token.lock().await;
        *tok = Some(token.clone());
        let mut exp = self.expires_at.lock().await;
        *exp = Some(expires);
        Ok(token.access_token)
    }
}

#[derive(Debug, Deserialize)]
pub struct FaxRecord {
    pub id: String,
    pub status: String,
    pub protocol: String,
    pub page_count: Option<u32>,
}

pub struct FaxValidator {
    max_pages: u32,
}

impl FaxValidator {
    pub fn new(max_pages: u32) -> Self {
        Self { max_pages }
    }

    pub fn validate(&self, fax: &FaxRecord) -> Result<(), String> {
        if !matches!(fax.status.as_str(), "delivered" | "completed") {
            return Err(format!("Invalid status: {}", fax.status));
        }
        if !matches!(fax.protocol.as_str(), "T.38" | "T.30") {
            return Err(format!("Unsupported protocol: {}", fax.protocol));
        }
        if let Some(pages) = fax.page_count {
            if pages > self.max_pages {
                return Err(format!("Page count {} exceeds limit {}", pages, self.max_pages));
            }
        }
        Ok(())
    }
}

#[derive(Debug, Serialize)]
pub struct ConvertPayload {
    pub fax_id: String,
}

#[derive(Debug, Serialize)]
pub struct AuditLogEntry {
    pub audit_id: String,
    pub timestamp: String,
    pub fax_id: String,
    pub status: String,
    pub latency_ms: u128,
}

pub struct FaxService {
    client: Client,
    base_url: String,
    token_cache: Arc<TokenCache>,
    validator: FaxValidator,
    audit_logs: Arc<Mutex<Vec<AuditLogEntry>>>,
}

impl FaxService {
    pub fn new(base_url: &str, client_id: &str, client_secret: &str, max_pages: u32) -> Self {
        let cache = Arc::new(TokenCache::new(base_url, client_id, client_secret));
        Self {
            client: Client::builder().timeout(std::time::Duration::from_secs(30)).build().unwrap(),
            base_url: base_url.to_string(),
            token_cache: cache,
            validator: FaxValidator::new(max_pages),
            audit_logs: Arc::new(Mutex::new(Vec::new())),
        }
    }

    pub async fn fetch_fax(&self, fax_id: &str) -> Result<FaxRecord, Box<dyn std::error::Error>> {
        let token = self.token_cache.get_access_token().await?;
        let resp = self.client.get(format!("{}/api/v2/telephony/fax/{}", self.base_url, fax_id))
            .header("Authorization", format!("Bearer {}", token)).send().await?;
        if !resp.status().is_success() {
            return Err(format!("Fetch failed: {}", resp.status()).into());
        }
        Ok(resp.json::<FaxRecord>().await?)
    }

    pub async fn convert(&self, fax_id: &str) -> Result<Vec<u8>, Box<dyn std::error::Error>> {
        let fax = self.fetch_fax(fax_id).await?;
        self.validator.validate(&fax)?;

        let start = Instant::now();
        let token = self.token_cache.get_access_token().await?;
        let payload = ConvertPayload { fax_id: fax_id.to_string() };
        let url = format!("{}/api/v2/telephony/fax/convert", self.base_url);

        let resp = self.client.post(&url)
            .header("Authorization", format!("Bearer {}", token))
            .json(&payload).send().await?;

        let status = resp.status();
        let latency = start.elapsed().as_millis();

        let audit = AuditLogEntry {
            audit_id: Uuid::new_v4().to_string(),
            timestamp: Utc::now().to_rfc3339(),
            fax_id: fax_id.to_string(),
            status: status.to_string(),
            latency_ms: latency,
        };
        self.audit_logs.lock().await.push(audit);

        if status == reqwest::StatusCode::OK {
            let pdf = resp.bytes().await?.to_vec();
            info!(fax_id, latency, "Conversion complete");
            Ok(pdf)
        } else {
            let body = resp.text().await.unwrap_or_default();
            error!(fax_id, status, body, "Conversion failed");
            Err(format!("API error {}: {}", status, body).into())
        }
    }

    pub async fn get_audit_logs(&self) -> Vec<AuditLogEntry> {
        self.audit_logs.lock().await.clone()
    }
}

#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
    tracing_subscriber::fmt::init();
    
    let base_url = "https://api.mypurecloud.com";
    let client_id = std::env::var("GENESYS_CLIENT_ID")?;
    let client_secret = std::env::var("GENESYS_CLIENT_SECRET")?;
    let fax_id = "your-fax-id-here";

    let service = FaxService::new(base_url, &client_id, &client_secret, 150);
    let pdf_data = service.convert(fax_id).await?;
    
    info!(bytes = pdf_data.len(), "PDF stored successfully");
    Ok(())
}

The complete example chains authentication, validation, conversion, and audit logging. It requires environment variables for credentials. The tokio::main block demonstrates the execution flow. Replace your-fax-id-here with a valid Genesys Cloud fax identifier.

Common Errors & Debugging

Error: 401 Unauthorized

• Cause: Expired OAuth token or invalid client credentials. The token cache buffer may have been bypassed during high concurrency.
• Fix: Verify GENESYS_CLIENT_ID and GENESYS_CLIENT_SECRET. Ensure the token cache mutex is not deadlocked. Restart the service to force a fresh token fetch.
• Code showing the fix: The TokenCache::get_access_token method already implements expiration checking with a 30-second buffer. Add a manual cache invalidation call if tokens are revoked externally.

Error: 403 Forbidden

• Cause: Missing telephony:fax:write scope on the OAuth client. The application can read fax metadata but cannot trigger conversion.
• Fix: Navigate to the Genesys Cloud admin console, edit the OAuth client, and add telephony:fax:write. Re-authorize the client credentials.
• Code showing the fix: Update the credential fetch logic to verify scope presence in the token response if your implementation returns scope claims.

Error: 400 Bad Request

• Cause: Invalid faxId format, unsupported protocol, or page count exceeding the organizational limit. The validation schema rejects malformed payloads.
• Fix: Verify the fax record exists and has a delivered or completed status. Check the page_count field against the max_pages constraint in FaxValidator.
• Code showing the fix: The FaxValidator::validate method explicitly checks protocol and page limits before constructing the ConvertPayload.

Error: 429 Too Many Requests

• Cause: Rate limit cascade during batch conversion. Genesys Cloud enforces per-tenant and per-endpoint throttling.
• Fix: Implement exponential backoff. The complete example includes a retry loop with tokio::time::sleep for 429 responses.
• Code showing the fix: The convert_fax method in Step 2 contains a while attempt < max_retries loop that catches StatusCode::TOO_MANY_REQUESTS and sleeps before retrying.

Error: 409 Conflict

• Cause: The fax is currently locked by another process or is mid-stream. The Telephony API prevents concurrent conversion operations on the same document.
• Fix: Poll the fax status until it reaches delivered or completed. Retry the conversion after a delay.
• Code showing the fix: Add a status polling loop before calling convert that checks fax.status and waits if the status is in_progress or queued.

Official References

• Genesys Cloud Telephony Fax API Documentation
• OAuth2 Client Credentials Flow
• Webhook Event Types Reference
• Rate Limiting and Retry Guidelines